Cornelis probably re-married? 31 maart 1614 (scan 12):

And (15 mei 1629):

The amount payed is considerable in both cases.

So this all looks consistent with a Cornelis Pancraesz being the father of "Pancraes Cornelisz Seijlmaeker of 17th century Alkmaar".

• Bought a house in 1587,
• 'schipper' in 1588,
• just became widower 1588; [Edit:] children stil minors.

So estimated Cornelis Pancraesz must have been born about [Edit:] 1550-1565. He possibly remarried twice after 1588: 

• wife + 1614 (the mother of Pancraes Cornelisz?) and
• widow + 1629.

So: if these are both his spouses, then he must have died between 1614 and 1629. [Edit] Which is (again) consistent with Bancraes Cornelisz owning the house ZZ verdronkenoord in 1628, supposedly inherited.

Marijtgen Thomis + 1586 (scan 119)?:

These children are "Pieter, Lijsbeth en Pieter Hijnedrix kinderen" which leads to the conclusion that Maritgen Thoenisdr was married to a 'Heijndrik' (Hijnedrik) before being married to Cornelis Pancrasz.

not quite correct, here the transcription of scan 47 Weeskamer Alkmaar :

Wij Doed Jans[zoon] Medenblick en[de] Cornelis Nanninx[zoon] schepenen in Alcmaer oirconden ende kennen dat voir ons gecomen ende
gecompareert es Corn[elis] Pancraes[zoon] Schipper onse mede poorter ende bekende mits desen wel en[de] deuchdelijcken schuldich te wese
Pieter, Lijsbeth en[de] Pieter [sic!] zijne drie kinderen geprocreert bij Maritgen Thoenis d[ochte]r zijne overleden huijsvro[u]we te samen de som[m]e
van twee hondert en[de] vijftich carolus guldens t'stuck tot XL gro[ten] vl[aams] den voirs[eijde] kinderen bij hem comparant ter presentie van
Thoenis Pieters[zoon] van Sinte Pancraes als bestevader van de voirs[eijde] zijne kinderen van haer smoeders zijde voir haer smoeders erve
bewesen , welcke voirs[eijde] somme hij comparant belooft heeft en[de] belooft mits desen sijn voirs[eijde] drie kinderen ofte elcx van dien zijn
gerechte derdendeel wel ende getro[u]welijcken uuijt te keeren ende betalen wanneer zij comen te h[u]welijcken ofte van hem gaen
ende belooffde voirts daerenboven de voors[eijde] zijne drie kinderen eerlijcken ende nae haren staet t'onderhouden in cost en[de] clederen om
behouden goedt tot hare mondige jaren toe. Stellende daervoiren ten specialen hypotheecke en[de] onderpande zijne camer met
haer erff staende ende leggende binnen deser stede aende suijdtzijde van Dronckenoirdt bekent met Aris Heijndricx[zoon] olijslager
aende westzijde en[de] de wed[u]we van Gerrit Sijmons[zoon] schipper aen d'oistzijde ende voirts g[ene]ralijcken en[de] specialijcken alle
zijne andere goeden roerende ende onroerende present en[de] toecomende geen uuijtgesondert omme alle gebreck van tgundt voors[eijd]
staet daer aen en[de] de keure van dien te mogen verhalen en[de] executeren, doen verhalen en[de] executeren als custinge willekens
maecxel ende heerlijcke schulde met heerlijcke en[de] reale executie van den hove van hollandt en[de] met ander sulck recht
recht, rechters en[de] executie alst den voirs[eijde] kinderen, hare voichden en[de] naeste vrunden tzelve alsdan gelieven en[de] goetduncken
zal zonder eenige desensie daer iegens te doen ofte te laten geschieden in eeniger manieren. Alles ter goeder tro[u]wen en[de] sonder
bedroch, des t'oirconde hebben wij schepenen voorn[oem]t elcx onsen zegel hierbeneden aengehangen opten XX Januarij a[nno]
XVc LXXXVIII in kennisse van mij secretaris

→ "Pieter" is named twice among the children, possibly in error

→ the maternal grandfather lives in St.Pancras

Deceased in 1661: Kornelis Bancrasz Zeijlemaker (scan 148):

(Grandson of the previously described)

Re: Peter, "not quite correct" => Thanks! 

1) So no Heijndrik as previous husband for Maritgen Thoenisdr. Maritgen and Cornelis Pancraes are the parents.
2) Timeline doesn't change a lot, maybe the estimate for Cornelis Pancraesz being born is now ~1555-1565, but that's all.
3) Surely, Pancraes Cornelis is born after 1588 since he doesn't appear in the 1588 document.

Quote Historisch Kadaster Alkmaar:

"Titel:1581.01.16 (NB. moet zijn 1587.01.15) verkoop aan Cornelis Bancrasz [...]"

So, supposedly, there must be a document based upon which the date of purchase of the house ZZ (Ver)dronckenoord is corrected from 1581.01.16 (from the document I found) into 1587.01.15. I have not been able to find that document. But it would potentially reveal relevant information as to the primary question in this string.

poorterboek 14.10.1581 [hier]

https://www.collectiegroesbeek.nl/doc/1150156 

Pancras | 1587-01-15
O.R.A. Alkmaar 133 fol 32
Achternamenindex
Cornelis Bancreas, groot schipper, koopt camer te Alkmaar

Here, scan 34

[Edit:] Transcription:

Cornels Bancraesz grootschipper heeft gecoft
van Jan Lubbertsz een vrije caemer staende ende
leggende ande zuijt zijde van Dronckenoort belent
met Arijs Heijndricxsz olijslaegher ande westzijde
ende Gerrijt Simonsz schipper ande oostzijde voorde
somme van VIc (600) guldens te betaelen meij ende? Ste Jacob
toecomende anno 87 ?ekken L (50) gul[den] ende voorts alle ???
daer aen? volgende ?ekken hondert ende de lesten
L (50) gulden stelt tot waer??? ????? ?? alles
volgende den bae?? besegel[ing] bij Corn[elis] Claesz
Dr??st ende Dirck Dircxsz Schepenen te Alkmaer
In daete den XVe (15e) Januarij anno 1587

I would be glad to receive any corrections, or additions (questionmarks) for this transcription. I think for now the only omissions are in the terms and periods of payment, and the phrases used to close the document

the will of Cornelis Pancrasz from 12.10.1604 [here], both a Pieter the Elder and a Pieter the Younger are among his sons and heirs, as well as a Pancraes Cornelisz.

as spouse is mentioned Geertgen Garbrantsd[ochte]r

So: Pancraes Cornelisz is born between 1588 and 1604.

Anyway, his mother then most likely is Geertgen Garbrantsdr. Lijsbeth must have died between 1588 and 1604 since Pieter 'the younger' and Pancraes are called ' sijn twee ander kinderen' if I am correct. And Maritgen Thoenisdr is the mother of both Pieters - we know that from the 1588 document.

Peter B. and Bart:  Thank you very much for the extensive replies.  WOW!  

On the house transaction involving Bancraes Cornelis in 1628, the Alkmmar archives posted them online today.  Here is the link to the relevant entry:

https://www.regionaalarchiefalkmaar.nl/collecties/archieven/archieven-2/scans/NL-AmrRAA-10.1.1.001/2.6.6.3/start/10/limit/10/highlight/1

P.S. Found this burial entry.  Unsure which of Cornelis Bancraes's wives this would be:

Die weduwe van Cornelis Banckeris Burial (15 May 1629):

https://www.familysearch.org/ark:/61903/3:1:3QS7-L9QV-TQ5C?i=62&cc=2037985&cat=230843

Re: Steve "Unsure which of Cornelis Bancraes's wives this would be" => the 3rd one we know of, we don't know her name yet...

Because Cornelis Pancraesz was "Grootschipper" I would expect he may be found in the (Danish) Soundtolregisters. Supposedly, there are records online starting with the year 1499 upto 1857. From 1574 on almost complete: 

"STR online has been started in 2009. We aim at completion by 2017.
RUG and Tresoar have outsourced the data entry to Breed, the social workplace of Nijmegen and surroundings, for the period of 1634 – 1857. Entry of the remaining data is organized via a crowdsourcing project, where volunteers do enter the data of 1499 - 1634."

and:

"The Sound Toll Registers (STR) are the accounts of the toll which the king of Denmark levied on the shipping through the Sound, the strait between Sweden and Denmark. They have been conserved (with gaps in the first decades) for the period from 1497 to 1857, when the toll was abolished. From 1574 on, the series is almost complete."

Since we know him as "Grootschipper" from 1587 this is at least over a decade into the "almost complete" period increasing chances of succes. Unfortunately, the database (and here) seems to be offline for now. In the not so distant past I've succesfully utilized tihs database....

And he may also be found:

Here. 1966 Stukken betreffende het Schippersgilde. 1608-1814. (not online)
Here. I.J Schippersgilde (Mostly not online)

I know that Leiden in that period did have different, separate 'gildes' for (ordinary) Schippers - small vessels, mostly rivers, lakes and some coastal - and (seagoing) Grootschippers. I do not see that in Alkmaar, but Leiden is much more familiar to me....

then there's a later version of the will dated 04.04.1614 [here] 

and 05.01.1626 when both Pieter the Elder and Younger have already died [here]

Look at the date: 4th of april 1614. In my mind there is now no doubt left at all that the deceased on the 31st of March "Die huijsvrou van Corn[elis Pancaes" indeed wás the wife of the same Cornelis:

4 days later...

====================

Cornelis Pancraes must have died not long after the 1626 will that Peter just has turned up: "[...] zieckel[ijk] zijnde, zittende bij de haert op een stoel [...]" (being ill, sitting near the fireplace on a chair). We know that Pancraes owned the house in 1628. Narrowing down the actual moment of Cornelis' death to just a couple of years.

There are quite some details about grandchildren to be found in this will, if my quick glance is right.

Stumbled across these items:

28 October 1603:

https://www.familysearch.org/ark:/61903/3:1:3Q9M-CSJ1-M33G-5?i=257&cat=2713215

Codicil:

https://www.familysearch.org/ark:/61903/3:1:3Q9M-CS8J-B3BY-T?i=17&cat=2713215

4 April 1614:

https://www.familysearch.org/ark:/61903/3:1:3Q9M-CSJ1-M33P-2?i=253&cat=2713215

5 January 1626:

https://www.familysearch.org/ark:/61903/3:1:3Q9M-CSJ1-M33B-B?i=255&cat=2713215