We booked Centerparcs for later this year around 2 months after we are due or second child and have since invited FIL and his partner to come with us. They live about 2hrs away and we don't see them as often as MIL and my parents. It only cost £30 to upgrade our lodge to include them - they've not mentioned contributing to the overall cost but we invited them so I don't really expect it. FIL is not my favourite person but I like his partner and I'm sure I can tolerate him for the sake of a weekend.
FIL has just texted me to say they're really looking forward to coming and have invited his partner's two children too. Before I launch into a full on hormonal strop, that's not really on is it? They're 21 and 17 so not exactly children incapable of being left alone for a weekend. They have never come to any family events we've invited them to before. It will cost us an additional £460 to upgrade again to a 4 bedroom lodge and if nothing else DP has met them once and I've never met them! DP thinks I'm being unreasonable to say no. I don't think I am, but I understand my hormones might be impacting on my decision!