OP I know exactly where you're coming from; my MIL is the same so here are some things I have used to make things bearable.
The Good Granny Guide by Jane Fearnley-Whittingstall (mum of that bloke who cooks in the Guardian) has loads of advice aimed specifically at the MIL, who is often left feeling a bit out of the loop as she is 'number two granny' after your own mum. I bought my MIL a copy to read. Don't know if she has or not, but it was a massive Please Just Back Off and Curb Your Enthusiasm request from me to her. Plus, DH saw it as me trying to reach out to his mum, which helped our relationship (mine and DH's) no end as I was getting so fraught with things.
Space. Your DH goes round to see his mum and sister several times a week, texts, calls, spends (to you) an unnecessary amount of time with them. Mine works with both of his parents so they see him daily, call him in between times and text constantly. This narks me because I personally think it's weird, but that is because they are not my family who do things differently. My advice to you here is let him go, but don't feel under any kind of pressure to have to go along too, and make his home with you and your new baby the most inviting place. You can't force him to choose between his 'birth' family and you, and trying to do so will only push him away. It will take a long time to bring him round perhaps, but can you really see him wanting to drop everything and run off to his mum when he could instead rush home to hold his child?
If you want to discuss how you feel with your DH (and I strongly recommend that you do, especially given your miscarriage and fragile state atm) don't back him into a corner by telling him his mum is making things hard for you. Doing this will make him have to choose between you again and isn't fair. Instead, tell him you feel very vulnerable and you need him to protect you from everyone/thing. Don't be too specific, just tell him your fears without laying them all at his family's feet. He gets to feel all manly and protective of you, and if he is anything like my DH, he will respond and protect you without feeling that his relationship with his mum has been compromised.
Finally (good lord I am sorry for rambling on so long!) it really will be better for you to get all of this off your chest and out of your mind as soon as possible so that you can enjoy the rest of your pregnancy in peace. You simply cannot afford, or be made to put up with the stress. For me, I had a few understanding female friends to whom I could tell everything my MIL was doing that hurt me, and they were all people who would not then go and tell her what I'd said. Use your mum, your friends, colleagues, whoever you can to get the harsh stuff off your chest and you will feel better when you go home to DH each night.
And can everyone please stop pictish bashing on this thread? There was a rather lengthy apology further up the the thread that people seem to have ignored.