Split custody, why get double health insurance for son?

Posting for a friend who doesnt have reddit.

Mom and Dad have a very young Son. They never got married, not together, and currently not living together. Mom lives in Missouri, Dad lives in Kansas. (Kansas City area, in-network always includes both sides of the state line.) They have a mutually agreed custody plan without ever getting courts involved.

Both parents have new jobs with insurance. Son is in Dad’s plan for 2023, Mom just for herself.

For 2024, looking at the numbers, Mom’s will be cheapest for similar coverage and is ready and willing to pay for Son’s coverage. Dad says they both need cover Son on their plans. Mom and I have no idea why that’s necessary.

From my own experience, that’s a bad idea. Due to an enrollment mistake on my part, I was briefly double-insured in January from my employers and the insurance I actually wanted threw a fit and was denying coverage until I told them the previous/old insurance processed (and denied) all claims that were incorrectly sent to them. I got it cleared up but that was a headache.

If we do insursance the way Dad says, I predict that headache is going to be a constant frustration. Also…its just more expensive to do things the way Dad thinks? They would both be paying increased premiums for having a +1 on their plan.

Dad’s defense is that he’s talking to “an insurance professional” of some kind he’s just doing what the professional is saying can be done. But why should you?

For the record, I’m close friends with Mom. Dad has no beef with me, but just hates being proven wrong. I’m suspect the insurance professional is legit but just trying to sell coverage because $$$.