I've posted about a similar issue before. Long story short both my BIL and his partner and me and DH have children with fairly serious (but different conditions). Our child is doing well but impact in future is uncertain. In laws child needs special schooling and childcare is mostly taken take of by other family members who are getting on a little.
We've been very cautious and had testing re having other children. My SIL 'accidentally' fell pregnant (within days of best friend who she copies in everything) even though they have 50% chance of same condition and no way to test.
We've tried to stay out if things except mutual relatives and family members are being taken advantage of despite being off work and perfectly healthy, my SIL has barely spent any time with her child who has special needs. The whole focus seems to be the new baby.
I'm completely fed up of their attention seeking (planning to tell me of the new baby at a small family occasion when everyone else knew and when we were going through genetic testing) and them palming off their child constantly. Plus they did nothing special for her birthday but planning an extravagant naming day for new baby.
I'm a bit miffed that my child isn't getting the same level of attention from family members who look after them but that's beside the point. BIL and SIL completely taking the piss and not bothering with the child they have and I can see the pressure on family members to increase even more. My DH was asked to babysit their new baby overnight (before the first scan and before I was even told) when the baby would only a few weeks old!
No one will say anything as they'll threaten to break contact with grandchildren. It's making me so cross. I have a terrible poker face and find it hard to bite my tongue!