lashaine,
Do you have a therapist/counselor? It sounds like you may need someone who you can call if you need support on this trip to see your son.
Sometimes people set up some things to help them stay safe when they must go on trips or go into unsafe places.
It helps to think through situations and how you will handle them BEFORE you get there.
You DO NOT need to see your ex-husband and his mother if you do not want to do so.
Try to think of ways to have time alone with your son to just be with him and shut out the annoying others.
On the trip be sure to eat, rest and sleep correctly to protect yourself physically from getting over-stressed. Take proper care of yourself.
When things bother you, REMIND yourself of why you are here and what you are accomplishing. It will help you stay strong.
I can't think of anything else that may be helpful to you, but I do wish you well and hope this trip is ALL you desire
Leslie and the Pixies