I can appreciate and empathize for your difficult family and cellular situation, but I would encourage you to keep the discussion on a single thread.
Once your phones are unlocked, you can grab prepaid service with another carrier. Your only option will be to get new phone numbers, as Koodo won't release the numbers from your ex-husband's account given the balance owing.
To confirm what you are asking, I've tried phones from various carriers on various other carriers on prepaid and postpaid. Once the phone is unlocked, you're good to go. The only exceptions are collections-blocking (which will prevent using your phone on the carrier who put the collections block) or blacklisting (which is limited to Canada/US and is only for lost or stolen phones).