It feels like the committee is being reasonable in offering a compromise but I can’t really see what’s in it for you. If, for instance, their repairs turned out to be bodgy, you would be responsible. I think a polite “no” would be an appropriate response. The problem lies with a previous committee that allowed a previous owner to do work without appropriate by-laws in place. It’s neither yours nor the current committee’s fault but there’s no reason for you to put your neck in this particular noose.