Ugh. I get it. May be useful to look at this in a pros and cons way:
Pros - S2 got to have fun with his cousins. Cousins are a valuable relationship for kids growing up. Also - S2 got to have some bonding time with grandparents.
Cons - you were inconvenienced. You are annoyed at ex’s family because of their lack of support (blood is almost always thicker than water, unfortunately) You don’t want to set a precedent of always having to be the one to do the work.
Hopefully this was a one-off because ex was out of town. And now that you’ve done it, you can feel free to turn down the next similar offer if it isn’t convenient for you. And be careful not to make ex’s family suffer for his sins - only for their own.
