SB's son JB is deceased. His son JB Jr. has a 723 cM,10% connection to me. JB II has a 361cM, 5% connection to me. Is it likely that SB is my birth father?
I find this quite confusing. Thanks.
I suggest you try DNA Painter's "What Are the Odds" calculator: https://dnapainter.com/tools/probability.
There are many online options to get help with your DNA questions in addition to DNAPainter suggested above. FamilySearch doesn't focus on DNA, and there are options that are much more private than this public forum.
@williamlucas5 I would like to refer you to this FamilySearch Community Group as they maybe able to help you with your question. You will have to join the group to post a question; there is no cost.
GENETIC GENEALOGY RESEARCH