If there is a Short Sale Addendum or an Addendum to Purchase Agreement, you are SOL.
Both of those forms build in protections for sellers in a short sale if a lien holder does not approve a sale in a form that works for the seller (like saying that the seller is still responsible for the deficiency).
It is possible that both the listing and buyer’s agent were negligent and did not provide those. In that case you might have some options.
If the lawyer you are using is anything other than a residential real estate specialist (like that is his entire practice) then you are SOL with atty fees.
If the seller’s bank declines this or puts non-viable conditions upon the sale, then really you don’t have a deal.
Even if you were to succeed in a specific performance lawsuit, the practical reality is that getting the crazy logistics of a multi-loan short sale working (without seller cooperation) mean your victory would be both Pyrrhic and pointless.
A better bet would be to get that atty you paid for to have a sit down with the seller and explain to him how hard it would be for Chase to come after him in a single action state and how his loan could be considered non-recourse (if that is a position that can be defended).