what do you think.., page-4

no, that is your role....as a primary care giver....IMHO

the MIL should shout,ie pay for you and your child to take the trip, or to accompany her on the trip...together with his mother, make it a family affair

there is no way I would allow an in-law to take my child
on such a significant event, away from me...
especially at such a young age...
after the age of 18-21 the child, would be able to make up their own mind, or choose to be away from you
the bond between the parents and child would be broken by such an event, at such a young age....imo

empathise, use empathy, and remind yourself...how would you have felt at such an age ???? if you were put in that situation...
your answer should reveal itself therein