When DH got with BM she also already had a child. DH never kept in contact with that child when they split. So I doubt I would ever be in this situation. But if it ever came up, I wouldn't allow it. Do you have children together? It's kinda like this... Would you want your child going with SS to BM's? I wouldn't! I understand they are half brothers and blah blah blah. But your DH isn't that kids father. SS and this kid should spend time together at BM's. I don't know. I may sound like a big bitch. But that's just my opinion!

I wouldn't have a problem with it as long as he was well behaved and respectful. He is extended family of SS's and if SS lives with you then he should be able to have guests. (with pre-approved permission) Just treat him as SS guest as you would any other like a neighbor boy or friend from school and give him the respect that any guest to your home would receive. He does not need to be treated like one of DH's children...as he is not.

How you treat is dependent on DHs relationship with him IMHO. If DH raised the kid as his own then I would at least welcome him as a family member of DH if not as a member of your joint family. I raised my SS as my own and had his mom and not continued our marriage or if something, heaven forbid, happened to her I would continue to be my son's dad.

At this stage of our lives my relationship with SS is independent of my relationship with his mother.

MMM also had a child before DH and her were ever together. My DH raised him,and was in every sense of the word his dad from the time he was aprox. 6-8 months old up to, well now (hes 20). I had been with DH for almost 8-10 months before I even knew that he wasnt DH bio son.So I guess its never been an issue for me, I just see him as DH son.
He has actually lived with us for a short period of time. I ex[pected the same out of him that I expect from anyone else staying in our house, that includes my own children. You follow the rules or your out!

It depends how close they still are, I would say that it would be good for your DH still to see him if he is close to him but outside the home. I understand it would worse then just your own steps, it really is like a spy to BM. I would say great take em to a ball game but not in your home.

Yes, it depends on the prior relationship. I was with my ex for 8 years, which at the time of our breakup was almost my daughter's entire life. He continued to see her along with our bio-son for every other weekend visitation for years. Now she's an older teenager and kind of outgrew the every other weekend visits, but they still regard each other as close family and his extended family includes her as well.

Ex has had a couple serious relationships over the years, and as far as I know those GFs were fine with my daughter. Of course they knew her from the very beginning...he didn't suddenly bring her over a long time into the relationship.