“I am going back to court with my ex to review his child support. He is saying that the kids spend more time with him than they actually do. Would it be wise to have my kids who are 17 & 16 write a letter stating how often they see their dad, for when I go to court in February?”
Generally, courts frown on involving the children at all. If they want to talk with your children, they will tell you. Keep in mind that the time that the children are sleeping at your ex’s counts as time for him.