If the developer sold you the property and it was recorded as owned by what ever corporation that you and your partner have, the developer has no "rights" to that property as far as I can see. I mean, YOU have the deed of trust, right?
The taxes were PAID, right? They are CURRENT, right? So the government has no reason to initiate a foreclosure...
I'm sure it was an oversight of some kind between ALL parties involved with the transaction - your lender, the title company, AND the seller/seller's attorney. If you purchased an Owner's title policy (as opposed to a Lender's policy), I think that would cover whatever claim the Developer may have. Although, I'm not sure you would have ANY obligation to them other than, "thanks"... Taxes are paid and you own the deed of trust... There was no WORK done so they can't slap you with a mechanic's lien... I mean, what can they do?
The RIGHT thing to do would be to pay them back for the taxes that they paid since the transaction was finalized. But I don't think they would have any reason to pursue any malicious action against you or your partner for an oversight that was clearly theirs (and the attorneys representing both of the parties in the transaction). I would DEFINITELY get an attorney to represent you, but I think you will be able to resolve it amicably.
For the record I am NOT an attorney. You should DEFINITELY retain one. But I think you will be ok.