Work place denying Health Insurance for step children

I live in Texas. I am a stay at home mom, married with 2 children from a previous marriage. Unfortunately, my children's father is not in their lives very often. I do get child support on occasion. My divorce papers state he is liable to carry insurance on the children....but he can not keep a job long enough to get insurance on them. My son has ADHD and is on costly meds. My problem is....
My husband (my children's step dad) is offered insurance through his job. We are trying to get my children on his insurance but his company is giving us a hard time about it. They want to see my divorce decree and saying he can not put the kids on the insurance unless we go get a court order stating we are liable for the insurance. This makes absolutely no sense to me at all. He provides over 50% of theirexpenses and the kids live with us 100% of the time. I am just dumbfounded over it. Can someone give me some advice on what we could do? We financially can not afford to go hire a lawyer over it but we can not afford to NOT have insurance on the kids either.

That depends in part what the employers policy is--is that laid out somewhere in your employee handbook or other location?

Any HR dept materials?