Friedrich Wilhelm Procknow

Baptism of Friedrich Wilhelm Procknow
born 12 days apart
Baptism of Henrietta Wilhelmina Procknow
Since we have baptismal records for both siblings this could be a case of superfetation. It is the rare formation of a fetus while another fetus is already present in the uterus.
https://en.wikipedia.org/wiki/Superfetation
"A 2008 French study found evidence to suggest that superfetation is a reality for humans, but that it is so rare that there have been fewer than 10 recorded cases in the world."