The condo docs should describe the situations in which the vote of the third owner can be overridden – structural integrity of the building, etc. If the third owner is overridden then they’d be liable for their share, with a lien on their unit.
And your can’t get blood from a stone, but there are a lot of reasons other than “i cannot get together that much money” why one owner might not want to pay up their share.
For instance, two owners may want to keep the house painted, and the other may be happy to pay less and live in a place with peeling paint.
I see people griping about HOAs all the time. I mean, real hate. How DARE anyone tell me what I have to do with my home!
If you feel that way, fine. But then you end up in a situation as you just described.
Informal agreements may seem more polite and less contentious but, when you have real assets to deal with, a formal legal agreement is best. It should protect everyone and clearly lay out obligations. Without such an agreement things can become a mess real fast.
Up to you which is worse to you.