Reviewing the available sources, I would like to propose that Christijn's sons appear to fall into at least 3 groups that correspond to different prospective partners:
1. Pieter van de Caep
Willem van de Caap
These two sons are recorded as "halfslag" in their baptism records (1692 and 1694), but there is no record of a surname attached to either of them. It is possible/likely they share the same the same unknown European father. FFY postulates that this Willem is the same person as Willem Stoltz. But that is problematic. It would mean Willem Stoltz married his own niece. Not impossible.......but hopefully not likely. There is also a conflicting death date and freedom status between Willem Stoltz and a published source (Campbell et al) for this Willem. So I think it best that this Willem and Willem Stoltz should remain separate profiles until the matter can be clarified.
2. Arnoldus Koevoet
Hendrik van de Caap
Arnoldus's baptism 1697 doesn't appear to mention if he was heel/halfslag, but Campbell et al suggest he was "heelslag". Hendrik's baptism 1701 records him as "heelslag". So both can be tentatively ascribed the same father.
3. Johannes Morgh and Andries Morgh (both recorded as "halfslag" in their 1703 and 1706 baptisms). Campbell etal refers to "Morgh" as a Dutch surname, so these two seem to be correctly grouped together as sons of ??? Morgh.