MIL and FIL both have problems with alcohol although they are very different problems.
FIL is alcohol dependent if he doesn't drink has the shakes ect. Drinks everyday and needs a drink to keep him level. He is an alcoholic. However because he holds down a full time, manual job (although has been on light duties since hospitalised 2 years ago with problems with his pancreas) they do not see his drinking as a problem. MIL agrees that he drinks "too much" but not that he is an a alcoholic.
MIL is an emotional binge drinker due to FIL being an addict their relationship has suffered and he has been mentally and financially abusive to her. She spends good portions of the year living (from Xmas to Sept on year) in silence and not speaking to him it's a horrible environment and I do feel sorry for her due to this but she will not leave him. we have tried but she won't do it. MIL can not be depended on to be done for anything, school plays, trips to B&Q, meeting in town for lunch it's a raffle if she will turn up sober or drunk. She is not alcohol depended as can not drink for weeks - sometimes months at a time.
Our DD's first Christmas was completely disrupted because of her drinking last year. On the run up she had been drunk when we had turned up with both grandchildren. Blind drunk slurring her words, falling about and giving DH an absolute mouthful of abuse about how he has never liked her
however DH brother begged us to go on Xmas but before we could even get there BIL called she was in the same state the turkey had been in the oven all night and burnt to a crisp there was no veg, or anything even in the house. We went last min to my mum who was thrilled to be having us and even fed BIL.
Over the course of the year I have kept my distance and been civil if need. I do not go when DH takes the kids to visit (he has only done this twice) I don't particularly want them going however DH has been struggling with his MH and the main thing is guilt about his parents so If he wants to visit and take the kids I don't stop him. Although this may be revised when they are older and more a wear.
Now BIL has had a daughter our niece, who we love dearly but he wants us all to go to MIL at least for a pop in so she can see all the grandkids at Xmas and we can all see each other.
I know she will be drunk... it's Xmas she wouldn't be able to not drink around people who are and FIL will encourage her as if she is drinking with him she's not moaning at him not to drink. We have been invited to DH cousin for dinner who we love and regularly socialise with we have agreed to go there for dinner which MIL will be livid about as her sisters will be there also.
So my AIBU is to put my foot down and say absolutely not, we're not popping in we're not coming near if you want to see you GC start making an effort all year round not just at Xmas. We're going to do what we have planned and that's it?