Hello James,
The original question came from me. Initially I was searching where and when Hendrikus Johannes Keulemans died. And through the help of several members of this community I found that four close family members Keulemans had moved in the mid 19th century from Rotterdam to Brooklyn, NY. One of these family members was Hendrikus Johannes's sister Johanna Jacoba Keulemans, who in the USA went by the name of Anna J. Van Santen.
Both the van Santen en Keulemans families in The Netherlands were Roman Catholic, so that wouldn't stand a marriage in the way. I believe that also the social backgrounds of both families were compatible. I don't know when and where the two met. This may well be somewhere abroad and the opinion and influence of the families was rather limited.
I didn't find proof of a marriage between Cornelius Christianus van Santen en Johanna Jacoba Keulemans in the Netherlands either and I am pretty sure they didn't marry here. This can mean four things:
1. I didn't search well enough and they did marry in The Netherlands after all.
2. They didn't marry at all and they just pretended to be married.
3. They married in the USA.
4. They married in some other country, e.g. Germany or the United Kingdom. It may be they sailed from either Germany or England to the USA and they got married before embarking.
I find option 3 the most logical. The couple may have met each other in the US and got married there, but maybe not in Brooklyn, but one of the other burroughs of New York. That is why my I asked whether anyone with access to Ancestry could find anything on them. Like immigration or naturalisation papers, or even a marriage certificate.
It is still not 100% sure that Johanna Jacoba Keulemans, born Rotterdam 20 March 1845 is the same person as Anna J. Van Santen, died Brooklyn 25 June 1890. But it is very likely.
I am really curious what information you have about the Keulemans in the US and I will send you a personal message with information I have found. Maybe we can help each other further,
Michaël Boers