In the two states in which I've had this problem, the court dealt with them differently.
In CA, the custodial parent had a heavy burden of convincing the child they HAD to go to ordered visitation. If the problem continued, and there was a history of interference (or such allegation) with visitation by the custodial parent, many CA courts will change custody.
I told clients to always do their best to have the children prepared and available for visitation, call the police when the children refused to go, and have the police talk to the children (and get an incident or report number, to protect yourself from claims of parental alienation).
If both parents were present when the cops were there, great. If the cops didn't want to come to house, bring the family to the police station.
Judges in Tx appear to tread lightly with teenagers - there is an implicit understanding that, at that age, it's hard to 'compel' them to go on visitation.
I've not seen a recent, local Tx case where the Judge changed custody of children (of those ages) due to interference with visitation (I'm sure there are egregious cases within Tx, but I haven't seen 'vanilla' cases with custody changed).
Additionally, in Tx, I don't know if the Sherriff/Chief would take the time to talk to children who didn't want to go on visitaiton.
I don't think you'll get very far with contempt charges in Tx, when the children are that age (but, who can, accurately, foresee what a particular Judge will do ?).
I think Mother's defense would be declarations from the children stating they won't go on visitation - which would just alienate Dad and children further, and cause the children to protect their Mother.
Why make the situation worse ?
OP, you only have a few more years to deal with ex regarding your children. From then on, you will be dealing, directly, with your children.
You should love your children more than your anger/frustration at your ex - spending 'alone' time with your children is just common sense - each child needs his/her Dad ... as though they are an only child (and each child should be treasured, separately).
They are not a pack of dogs you put together to walk at the same time. Each child is anxious to be recognized and loved, separately.
What is your issue, OP ?
Winning and prevailing over your ex ? or,
Loving each of your children and ensuring each child knows how special s/he is, and how much you love that child and treasure him/her ?
What's the big deal about showing each child that you love them, and making sure each child has 'alone' time with you ?
They are, each one, growing up fast and won't need you, as much (if at all) later in their life.
