Grandma and Grandpa want 17 month old to sleep in their bed during sleepover..? Baby has never slept away.

Guys.. my husbands parents are so sweet. They are the best in laws ever and I want them to spend time with their grandkids. We don’t have any other family who can help us. our son has asthma and also very severe separation anxiety and his parents are in their early 70s also not really very strong and capable (his mom sometimes has to use a wheelchair when in places). They’re both well over 250-300 lbs each… anyway they really want this night where all the grandkids sleep over. And I understand because they are both in poor health and we don’t know how much longer they’ll be with us. This would be very special for them and they’ve been talking about it for a while. I agreed to the sleepover only because I just I want them to spend time with the kids and they begged.. well our 17 month old still wakes up several times a night and cries if he’s not being cuddled (we co sleep) so grandma asked if it was okay if when he stays there for the sleepover if he cosleeps with them. I’m worried because I know they are hard sleepers, grandpa uses a cpap and they often drink a LOT, they’re both very overweight and I just feel it’s a recipe for disaster but I really don’t want to be the bad guy.. I’m also a bit worried for our sons safety. How should I handled this? Should I just let it play out and hope for the best? Should I say you know I don’t think it’s a good idea and upset everyone? I honestly in my heart feel him sleeping over there he’s going to cry the whole time too and I worry that it will distress him so much. He’s never slept away from us. And I do worry for his safety if he does end up cosleeping with them. I also want to emphasise how much this will break grandma and grandpas heart if I tell them he can’t sleepover. I’m not sure what to do. Maybe my fears are irrational? Help!