This threat brings back so many memories. My eldest DS was in exactly this type of relationship and had a wife and mother in law of the same ilk. Anything I did was twisted and used to make it look like my intentions were to upset them. Buy a gift, it's done to upset them. Pay for meals out
just for them, I supposedly picked the restaurant to embarass her somehow. Call up to ask how the pregnancy was going, I'm harassing her. Don't call to give them space, I don't give a damn about whether or not she miscarried, not that that was ever a concern during the pregnancy.
When they announced her pregnancy, myself and my husband called to congratulate them, as we knew she was looking for any excuse to cut off contact with his family, as she'd made him do with all his friends. Inside we were gutted though as we'd already witnessed the way she treated our son.
Her and her mother did turn him against us and he ceased all contact for over 3 years. Apparently my congratulations weren't quite effusive enough, so I obviously couldn't be part of their child's life, as I didn't earn my place in theirs. That came after we'd furnished the entire nursery, bought the pram, car seat, bouncy chair, sterilisation equipment and a wardrobe full of clothes, everything they'd said they needed. They allowed us to meet our first grandson just once, accepted all the flowers, the box of nappies etc etc, then cut us off completely.
Three years later the relationship was over. As expected she refused to allow our DS to play any part in the child's life thereafter, and actually claimed he was the result of an affair and not our DGS at all.
Sometimes you can't win whatever you do. I've learned that you have to stand up for yourself because becoming a door mat for someone like that really won't get you anywhere.