Does your decree not specify which of you is to carry it if you both have it available? Does it not address how to handle such a situation depending on cost and coverage?
Your decree needs to be reviewed. If it does not contain those provisions, then you may need to modify the decree. And yes, in general, if one can obtain equal or better coverage at less cost then that could become the primary with yours being a secondary insurance, and the contributions paid by each of you appropriately set off.
Based on what you say, you don't have an attorney. That is a big mistake.
You really need to get with an experienced family law attorney just as quickly as you can to review the facts of your case and set out a plan to assert your position. Please understand that this site does not allow us to recommend any particular attorney or firm, but I do know what a mess these cases can be having handled many disputed matters. Do your on-line research and look for attorneys experienced in these types of matters.
Answered on Sep 12th, 2017 at 7:29 AM