My lessons were:
1) if you’re going to accrue gift cards for hardware purchases, use a separate Apple ID. Do not use that ID for anything else and especially not as family organizer.
2) save paper trails for all your gift cards. That’s your only way out of this.
3) be prepared to be treated like a scammer by Apple Support. They will even question where you got the devices you traded in at the store. Some support staff will basically say you stole them without any evidence.