"Can you advise where to go from here?"
The owners need to band together and form a cohesive, cherent, educated group. You probably need proper legal advice. This will cost money.
Your post reads too much like an us ( owners) (passive) and them ( receiver, builders) and not enough active - we (owners) must sort this out, as best as.
I see this in practice all the time- so many people just don't get it, they think "the man" needs to get his act together and sort it out. They don't get that they need to work together, they need to accept responsibility for what is happening to them.
mf