My DH is 30- his parents split when he was 1 when FIL had an affair with DH's now Stepmother - they are now married with two sons of their own (20 and 17). DH and I have been together 10 years, married 5 and our DD is 7. FIL and his wife have never babysat, offered to babysit, shown any interest in DD's life or ours as a family - they were vocal they wanted us to have a boy. They kicked up a fuss when we got married that they had to sit on the same side of the church as DH's mum's family and then left at 7pm (we got married at 3.30pm) so Step-MIL didn't have to spend evening with MIL who didn't give a shit if they were there; she was enjoying her son's wedding
Things came to a head a bit a couple of years ago I passed a postgrad and my GM made a comment on social media about how DH's family should be glad I'd bought some brains to it - I'm not sure why - I've never said they were stupid or anything; just GM thinking I'm the bees knees [and she is a bit nuts]. I called her out on it and apologised to DH's stepmother who was offended. That Xmas she asked us not to come over because "they wanted a family Xmas". 
Since then I've seen them twice (they live 5 minutes away) and each time it's been uncomfortable. I make sure I buy birthday cards/presents/xmas presents etc for FIL, Step-MIL and the two boys but I post them as it's clear we're not welcome there for 'family occasions'. FIL phones DH to thank him but it's transpired he can't call him in the evenings when he's home as step-MIL says it's "family time".
I've asked DH why he puts up with it and he just thinks sun shines out of FIL's arse and it's not his fault step-MIL wants to pretend my DH never happened as he's a reminder of the fact he came firstI think he needs to grown some balls
The straw that broke the camel's back for me came this weekend. DH and I went out for dinner and the whole of his dad's side of the family were out at the restaurant celebrating his GM's 90th birthday (we'd sent flowers- we'd not forgotten). We hadn't been invited as it was "no kids" - ironically we were out without our DD as we have the ability to book a babysitter or ask one of her nice grandparents but we weren't even asked.
I'm so upset and can't work out what I've done to make them dislike us so much. I don't care if DH wants to keep in contact - I'd rather he did to be honest but I can't be arsed to try anymore and I'm wanting to go NC before DD realises she's not particularly welcomed. It's step-MIL's birthday next week and I don't want to buy a card and present or pretend I give a shit anymore.
I seriously thought about burning my bridges and writing to tell them what awful people they are but it won't achieve anything and will only give them a reason to say how awful I am. WIBU to just go NC and let my DH decide if he wants to carry it on?!