Sounds like your bosses are in a tight jam at work which really sucks. I'd go into the conversation with a potential solution...your mom takes care of then for the week, your mom takes then at your house for the week, you post on a neighborhood list serve and find a family who's going out if town and has a nanny needing work etc. If this is needed surgery that can't realistically wait six months until their bosses don't hate then anymore, then you need to do it, but I'd be offering them solutions not more problems. Ultimately this is your problem too since it's your job and theirs in the balance.