K.N.
I'm happily married and 18 weeks pregnant with baby number 5, and my mom won't speak to me right now either because she doesn't think we need 5 kids. Don't let your family ruin this for you. You are an adult and your life is yours. Unless the people complaining are raising or supporting your kids they have no say.
As for the rest, I m/c'd twice before my 4th child, so we waited till about 14 weeks to share the news, and like you I told my mom first and it really did make it so much harder then to tell my older kids (number 4 is only 9 months old so he doesn't care, lol), but they took it well. I'm also showing, and very obviously pregnant which is the only reason I told them when i did. I'm happy they know and are excited and it's really helped me deal with other people being stupid and nasty about it.
it sounds like your daughter wants a sibling, so share your joy! with my 4th the kids went to my ultrasound, my only daughter cried when she heard it was another boy, but otherwise it was a GREAT day for all of us and I'm so glad they were there. I like when they ask about the baby and what is going on and when we find out the gender and that they want to shop and joke about names. So really don't hide it from her just because other people are being dumb. And complicated or not, you've made it this far and chances are baby is just fine, You can't spend the next 22 weeks scared something is wrong, I've done that, it doesn't do any good. Good luck! and congrats!!!! Nothing matters more than what you feel for this baby, sure family should be supportive, but when they aren't they aren't worth your time. you have your own things to focus on.