Tristan's trip

Why are the useless adult kids tagging along?

If this year was meant for memories why does Tristan have to share his memories with other people?

And why was Max allowed to book his dream activity? It doesn't matter if Tristan like; it's that it was someone else's dream and not his.

Lastly, if Crystal had months to prepare the trip why did she not work to get Tristan a passport?