According to the book that Peter provided a link to, both graves should be located 'in a garden, outside the town' - in these days that is. So that should be a garden (what it is today is anybodies guess) in the proximity of the old town or village.
The book says that on the stone on Nicolaes Faber's grave the following epitaph can be read:
Die veel met jok, en ernst, versleet zijns levens uyren,
rust in dit donker graf, en word der wormen spijs,
Zijns levens vreemdigheyd zal vele jaren duyren,
De ziel omtfange God by hem in't Paradijs
(Translated, and I am not a poet:)
He spend the hours of life with gravity and fun,
Forage for the grubs, resting in this murky hole.
Remember the weirdness of his life for years to come,
To be in Paradise may God receive his soul.
The grave of Abraham van der Voort (still according the same book) should be 'opposite' of Faber's grave, and with the following epitaph:
Een die van Imborst goed, noyt twist, of onheyl baarde,
Rust onder deze zerk, en word tot asch, en stof.
In't beste van zijn jeugd verliet hij ons, en de aarde,
Zijn ziel hier boven in den hemel zingd Gods lof.
(Translated)
Righteous character, never causing harm or strife
Resting under this stone, ashes to ashes, dust to dust
He left the earth and us in the prime of his life
In heaven above his soul sings praise to God he must