Yet another vote for Doctor Who. You can’t hide from family, so be honest with them, and I’m sure your brother will appreciate it and will be pleased for you, even though it’s difficult for him. There’s no need for any big announcement - let the news filter out from the people you tell. And (assuming) he knows exactly what happened with you in January, he has an understanding of what it’s like to be on the other side of the conversation.
crazyjoe, you’ve made a good choice. Your sister-in-law will have a chance to adjust to the news in private. She and your brother can get through this just as other couples have. Your thoughtfulness for their feelings is very kind.
And congratulations!