Sorry but no matter how YOU feel about the situation, the truth is that your sons do indeed have a half sister. Therefore, they have a sibling...a sister to be more exact.

Why would your DH take YOUR kids to BM's house? That's just weird.

She's their sister. Half-sister. Sticking your head in the sand doesn't change and you are shortchanging your own sons by attempting to deny it.

She is their half sister. What you can ask him is not to take the boys to his exs house as she is bat-shit crazy. SD can come to your home. But in the end he is just as much entitled to take his sons to any place he may do so legally as you are.
The trick is to get him on your side to keep the Ex at armslength. However consider if he didn't want you to take his sons around your uncle Bob because he doesn't like him. WOuld you do that? Deny your sons the chance to meet and interact with Uncle Bob just because he said so? Would that be fair? After all, he is your family ... just as this girl shares half her DNA with your sons. Then we get back to the kidney transplant scenario...

Firstly, its odd that he goes to BMs house to see SD. Why doesn't she visit your joint home?
Secondly, I don't care what people say about half siblings, if I don't want you to take my child to your ex-wife's house, you aren't going to do it. End of story.

There is no reason in the world that ur dh needs to be "playing house" at the bm's house. I'd nip that sh!t in thee bud now. When I first got w my dh he would walk ss10 (at the time) to the door of bm's for a chit-chat. Um....no.
Bm also got pregnant by a guy w a tear drop tattoo while in rehab and still married to dh (at the time). So ss has this half-sister that for some reason my dh loves! Constantly is talking about ss's "sister". That's NOT HIS SISTER! Its his HALF SISTER. It's his bm's responsibility to see that they get "bonding time" when as is at HER house. Period.