So she's keeping the kids from him for "lying"

So this weekend my boyfriend was supposed to pick up his son and daughter for the weekend and drop them off on Tuesday. Well I guess him and his ex have been going back and forth about medical insurance. They used to be married but are currently going through the process of divorce and custody. Through state law it's required my boyfriend cover the kids medically, which he does since he's retired army. Well he thought that they also had dental. He thought he was covered for dental, especially since he's had dental work in the past. Well as it turns out nor him or the kids are covered for dental. So his ex is taking that as he's lying and she can't trust him with the kids. She does have full legal custody (because my boyfriend was a truck driver at the time and thought that made more sense to give her those rights. I tried to warm him not to do it but he did it anyway) so now she wants the kids back Monday morning which is our baby shower, which she knows about. She's being so petty right now at the loss of the kids, all over a misunderstanding. And while yes she has legal right to do what she's doing it doesn't make it right. She's taking the kids from a celebration of their brother and a chance to see family and friends they rarely see, not to mention their dad who they only see a couple days out of the month because that's all she allows. He wants to be in their lives and is seeking a lawyer for help. I really just wanted to rant because not only is he upset but so am I. I specifically planned this celebration so I had my kids (which I share 50/50 with their father) his kids haven't seen mine in months because the schedules haven't matched. I'm angry and sad and can't understand her thinking. I really just wanted to vent and rant about it.