Hey Evan,
Is there a reason why you're moving out? I know it can be frustrating when people struggle with pronouns, but generally that does improve as they see you more often, especially as you're continuing to masculinize.
I agree with Ms. Grace's assessment. Imagine how you'd feel if she had a secret and you found out from someone else instead of her. Unless your intention is to move and never talk to your family again, I think it's easier to just have the conversation and work towards helping her understand.
As far as her husband, a lot of people are homophobic and transphobic before they meet someone from the LGBTQ community. Often times after that, they find it hard to reconcile the things they believed us to be with the reality of what we are. While it may take some time for him to come around, I wouldn't immediately write him off as a lost cause.
Best of luck to you, friend.