"If he decide he doesn’t want to be around relatives then that’s his problem, not theirs"
No it bloody isn't. You have to do things at times to suit your children's needs.
Even non resident parents.
The Teen years are tough for everyone. Girls need their Mums at times, but they also need a goid relationship with both Parents.
Likewise, Lads need their Dad's, not their StepMums.
Depending on what's going on in your Teen's life, sometimes you have to take time off work, cancel holidays and concentrate on them.
What Mother would go on holiday without her Teen Daughter, who is having anger issues and then just go straight to working away?
They wouldn't, unless they are happy to help fuck up their mental health.
"he is resentful of the easy time we have, compared to his Mother"
I'm not surprised, you are living the typical 'Disney Dad', piss off and leave the Mother to it, lifestyle.
Good on your SS (let's face it, he isn't a DS's) for recognising that. I hope he gets through this tough patch.
Did you post about him suddenly not wanting to go?
Many on that thread felt his Dad should give him more time than he has been.