Compulsory holiday with in-laws?

My mil who is widowed turns 70 next year and wants us to all go on a week long overseas cruise with her. I will have husband and 2 kids under 2 and my sil, her husband and two kids are also invited. This is apparently a dream of mil, and a once in a lifetime experience for her. It will cost us between $10-14 k. This includes flights to the port and then a suite as I can’t have my infant children sleeping on bunks. I suspect my mil is paying for my sil and her family ( I could be wrong). My mil is comfortably off and can afford to do this. We are also comfortably off however we have a huge debt which we are paying off and while I think they all assume we have lots of money, I feel a bit peeved I have to travel on a holiday I’m not interested and drag two kids around ( I haven’t done a holiday yet with them as I wanted to wait longer- they’re too hard to juggle) . I raised this with husband who told me how this is her dream and she’s had a hard life and that fulfilling a family holiday for her would make her so happy.Am I being selfish or are my $ concerns valid. I would probably suck it up if I felt she was contributing to it.