@MILissue I'm going against the grain here and don't think you should go for 50/50 next year. Everything these days is about splitting everything "fairly", but honestly, when it comes to children, I do think it's better for them to have one main home. Children can find it so unsettling with 50/50 arrangements and I feel for them.
I do think that as you have such a good relationship with the child's mother, that going for 50/50 may jeopardise that (unless of course she actually wanted that too). I'm just thinking from my point of view, I'd be devastated to go from practically full-time custody to only 50%.
Your DH can continue to be a father, co-parent with her mother, contribute financially, and keep his work commitments with the current schedule, perhaps introduce a third night so it's 6 nights per month or something. It has to work for both families, yourselves and the child's mum.
Anyway, I know the thread wasn't about that, I just didn't like reading so many people laying into your husband for not taking the child's mother to court for 50/50 🙄
In terms of your MIL, as you know, she'll never be happy. Personally, I'd not give her any overnights, and keep to what contact you and DH are happy with, if that's MIL joining you all as a family for one afternoon per month, then so be it. Your DH can shut down any whinging from her. As for your baby, not a chance in hell I'd let my baby sleep over with anyone, but especially not this overbearing MIL. I actually hope the child's mother stops contact between SD & MIL on her time. MIL sounds like a pain in the ass.