I'm with mikelz777 at this point. Time to walk away.
You have already done more than could reasonably be expected of you. No good can come of continuing on this path. The decision and its consequences must ultimately be theirs, not yours.
Say it with me, "I've given you all the advice I can. Instruments are personal, and this is your ukulele, not mine. You will have to make the choice for yourself."