Kate I agree with Chrystal. You have no obligation to tell him - because the usual rules don't apply here. Of course normally you'd feel you should inform your dc's dad that your dc is going to have a brother/sister. But these people over step the mark all the time and treat others with contempt. I believe therefore you treat them just the same. Ice cold civility when necessary - and only the civil part because it benefits you to remain the same reasonable person you know you are.
No contact unless unavoidable, and only then in writing - text/email/notes etc. Don't have their words inside your head, don't speak to them. Forget everything you've been told about dealing with people, and forget about trying to protect his image as regards your dc. It can't be done. She knows what's going on, she knows you're the truthful one.
As for telling his family. They should be ashamed to be related to him. I don't know what kind of relationship you have with them but again, I wouldn't bother. Personally I think you have every right to withhold contact once you get your dd back. Let him argue in court as to why he's a fit parent. I know there are some awful outcomes on here, where it looks like the court would have naturally found against the WN but haven't. But surely with his history he has to be stopped.
Also re his family. I think you said earlier his contact is supposed to be supervised via/with his mum. Well, she's doing a cracking job isn't she. So again, why would you feel obligated to tell her about your pregnancy.