What you have, to use the right legal jargon, is a breach of contract. You can sue for everything you put into the lot, plus interest, taxes, mileage, etc.
Here's the big problem you are likely to encounter - you could spend thousands on legal fees and win your case, and the developer could just turn around file for bankruptcy.
I also wonder why the previous attorney wasn't making progress. It's possible you had either a bad case or a bad attorney. Your case sounds solid to me, but, on the other hand, I've only heard one side of the story.
I would suggest scheduling a paid, 1/2 hr to 1 hr consultation with the previous attorney (unless you think he or she is worthless) and find out exactly (more precisely) what the status of the case is, including challenges/obstacles. That would be a good starting point.
After that, you can try to pursue the lawsuit yourself, or with a different attorney.
As I said above, you sound like you have a solid case (no pun intended), but no matter what the developer promised, if he or she has no money, you and the other owners are going to have to pay for everything yourself.
Another option is to sell the lot at a loss OR sell at a loss, take a contract, and make a little money on, say, 7% interest.
You have a bad situation. There's no way to say that any differently.
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Thanks, XXXXX XXXXX sure wish I had happier news for you.
Jane Doe Deer