Seller Breached Contract

My wife and I are currently dealing with a seller who is breaching the contract. The house we are trying to get sits on a half acre lot and the lot next to it was listed as coming with the house. So in total it was listed as 1 acre. This is why we went under contract because of the extra land. On the day of closing (like we are signing papers in front of the lawyer) he sends the deed in with only one lot. The actual contract was signed stating both lots by the seller. He tried to state that he was going to build on that land and it was not part of the deal and was an oversight on his part and his realtor messed up the listing.

He kept going back and forth on whether or not he was going to go through with the contract to the point we have a signed deed with both lots. And the very same day he wrote a termination letter and tried to give us 5k.

If we decide to get a lawyer how long would this process take? We truly love the house and see this as our forever home.

Any advice would be greatly appreciated.