New Stepmom and recently pregnant. Help!

Hey everyone! Happy I found this community. I have two step kids that I love a lot. Like so so so so so much. But their mom has become increasingly difficult over the 5 short months I’ve been married to her ex and their dad. I love my husband and my kids but sometimes I lose my mind over how poorly they treat us. Like really angry. Especially at the oldest as he’s become “mommies minion” and has tried to dictate how we run our home and boss his sister around on his mother’s behalf. Like such stupid crap. Like painting her nails or what kind of chicken nuggets they eat. Or what kind of milk they drink. I know she coaches them because at this point I can tell when they’re saying what she wants them to say because it’s just literally the same ugly stuff she’ll email/texts. And they do just straight up tell us what ugly things she says. I’m also pregnant and really worried she’ll use my pregnancy to hurt the kids. She kind of did it in regards to wedding and now our marriage. My questions are :

  1. How do I get over the nasty things his ex does/days to my husband?
  2. How do I let go of her manipulating the kids?
  3. How do I include them as much as possible in this new chapter of our family?
  4. And finally how much should I pursue them?