My question involves a child custody case from the State of: Utah
Some background. My sister was recently divorced and was awarded full physical custody and joint legal custody with her now ex over their 5 children. Her ex chose to hide after she filed the petition for divorce and refused to be served notice of the filing. Much of the language in the decree favors my sister because of this. Her ex was living in a different state with his parents(or somewhere) at the time of divorce but recently moved to within a couple of hundred miles of my sister and the kids and has just recently started exercising what little parent time he is actually entitled to.

Most of the language in the decree related to parent time and visitation simply references the utah state code governing such matters. By that language her ex is entitled to 4 weeks of extended parent time in the summer with 2 of those weeks being uninterrupted parent time.

When discussing his summer parent time, the kids dad informed my sister that the kids would be going to his parents house (grandparents) for 4 weeks straight in the summer. It should be noted that the grandparents live 1500 miles away from where my sister lives and 1700 miles away from where the kids dad now lives. He does not plan to be there with the kids during this time. He basically wants the kids to have a summer vacation with their grandparents but he doesn't plan on being there at all.

My sister is refusing to allow this to happen basically on the principle that if he isn't going to actually be with the kids then she has the right to be with them per the first right of refusal language in their decree.

Reading over her decree and how parent time works I don't think he can just ship the kids off to their grandparents home for his summer parent time. I also don't think the language allows for his parent time to be 4 weeks straight as he is claiming. Is there something related to this that I don't understand?