This isn't so much an AIBU as a rant as I know I'm probably being a bit U, but it's just getting to me today.
It's my DS's Christening on Sunday. Much later than planned as it was a struggle finding a time that all GP's could manage.
PiL have not seen DS since he was just under 8mo (he's 1.1 now). To be fair, we did plan to take him away on holiday in the summer and stop off at them along the way (they live about 500 miles away) but the heat, DS not coping with it in his buggy, DS being difficult with food and various other things meant that we decided to stay home. In the event, they went on holiday to a destination about 150 miles away, but despite DH suggesting meeting half way so they could see DS it didn't happen.
So now it's their first grandchild being christened and we invited them up to ours after the event to stay for as long as they wanted (he is being christened in my home town as the majority of friends/family are there) but they have declined this. In fact, they are planning to arrive on the Saturday evening and leave early Monday morning.
MiL is a teacher so will be on holiday and FiL is self employed so not dependent on a holiday rota.
I know I can't force them to visit but I feel so hacked off on behalf of my DS that his GP's are essentially going to be strangers to him at his christening 
But what really gets me is that MiL has started making pointed comments about my dad and stepmum seeing DS so often. They live abroad, and have the same holidays as MiL, but they come home every holiday to see us and DS (at quite considerable travel expense). However, I have tried inviting PiL up to visit several times and it gets met with a "maybe, we'll see" response.
I just don't know what else I can do to encourage them to visit. It's an open family so I know it's not money related. DH's work means going to them isn't an option so it seems that DS will be missing out.
So I guess I'm being U in expecting them to visit whenever they can, but NU in minding that they don't 