Oh boy, this sounds soooo familiar to me. Why is it always the ILs????!!!
My MIL tried to take over during the pg (first grandchild both sides, but my Mum was the best!), I spent most of the time 'managing' her expectations and they still came crashing down after DD was born. She threw a big tantrum, had a huge argument with DP (thankfully, not me) and didn't speak to us for 6 mths! Bliss! Didn't last, but she is better since. Our boundaries are VERY CLEAR. She causes grief, but it's contained and controlled and has minimal impact on DD, who loves her Grandma. DP's brother is finally having a baby with his fiancee and this may or may not take the pressure off us! (MIL says she doesn't care what this baby is, as she already has her much-wanted beautiful granddaughter...).
Your DH needs to stand by you and respect your feelings, in spite of his family. You and DS are his family now, the extended family needs to respect this and take the backseat supportive role they are meant to. They've raised their children, it's time to wait and be asked for what you need, not do it for you. DP always did this for me and despite the problems his family caused in our relationship, it would have been MUCH worse had he not been so clear and supportive with me.

