I think your mil and my mil maybe sisters. 
You have to bite the bullet and regain some distance from her. Start locking your front door so she can't just walk in.
Anything she buys you, don't except or leave in the bag but that applies to everything . She will soon get the message.
I could have wrote your post. My mil is like that dp. When I first met mil, she told me that she would always be number one in his life. She was wrong.
You dp also has a role to play in this. He is enabling her to behave like this and ultimately there will have to be a choice made, you or her.
Dp and I went through this when I was 8months pregnant as both of them assumed she would be present at the birth. I basically said, he could leave if he wanted as I wasn't going to live my life being undermined by her OR him. He choose me.
Things are better BUT she still has her moments.
op you have to look long n to the future and see want it holds under the status quo and set your stall out accordingly .
Also be very wary of your ds around this woman as she will see her self more important n his life than you are.
Dp speaking to you like that is not on. If that's his normal attitude towards you, I'd be thinking of getting the hell away from them both