Need unbiased input

In 2 months, my older son and his wife are going on a 6 day trip to a tropical island with his company and won’t take their 16 month old baby with them. My husband (who is not my son’s father) and I live in the same town as my son and his family, but we spend 4 months in the winter out of state, 1300 miles away, so we won’t be home yet when my son and his wife go on this trip. When my husband and I leave for the winter, we are generally gone the entire 4 months and see no need to return except for an emergency, such as a death in the family.

My son’s mother-in-law and father-in-law are divorced, but also live in the same town. At the holidays before the baby was born, the MIL returned to our town from living out of state for about a year, moved into the house with my son and DIL, on the condition that she would provide full time daycare while my DIL worked at home. Also this was supposedly so my granddaughter wouldn’t have to be in daycare until she was a year old. I say supposedly, because my DIL worked at home, and did a lot of the childcare that a real in-home sitter would do, while also working. The FIL comes over every day to bring carry out breakfast and/or lunch and to assist with childcare. (He’s very good with the baby.) My DIL and the MIL have demanded that my son take off work every Wednesday so the MIL can have a day off.

My son has asked me to return from out of state for a few days to help care for the grand baby while they’re on the trip. They have daycare for the baby 3, and possibly 5, of the days while they’re gone. The care needed will mostly be evenings, overnight, and transportation to and from daycare.

I do not want to return from our 4 month winter trip for a week, or even a few days, to pitch in on the childcare while my son and his wife are on their business trip, and I’ve told my son this. My DIL is apparently giving my son a lot of grief about this, saying that I don’t help out as much as her parents. Since her parents are right there in town and are very familiar with caring for the grand baby, I think they should do it. Additionally, throughout the year, the MIL hasn’t really held up her end of the agreement of providing daycare so she could live in their home. If this trip were occurring at a time when I’m in town, I would help with childcare, no problem. The issue is returning from our out of town extended stay for a week, then going back for a couple of weeks, then coming home for the summer.

So, do you agree with my position that I don’t want to return from out of state to help with childcare while they’re on the business trip? More importantly, long term, how do I deal with the fallout from the DIL, MIL, & FIL if I don’t come back to help with childcare while they’re gone? ‘Cuz I know they’re gonna be gunning for me.