Land takes a long time to sell and lots of work. Since you vest in a business entity and it's raw land residential real estate rules are not the same as commercial (even though is zoned residential The disclosure you mention doesn't need to be signed and disclosures are often re-provided at closing to cover all bases, it's a he said she said- he will say he gave it to you twice.)
Attorney fees you will pay up front perhaps $100000. If agent is part of corporate brand they have in house almost free.
You have mediation in the listing agreement? It's going to be an agent who may not see you in the light you wish to be cast.
If goes to jury trial you need every piece of paper in order and it will come down to who they like better, (really all in the emoticons not the facts because contract law is boring to a jury).
PA law is vague as too what is commercial even if you intended to build residential units on the vacant land.
The term "commercial property" means (1) any building,
structure or facility, or portion thereof, which is used,
occupied or is intended, arranged or designed to be used or
occupied for the purpose of operating a business, an office, a
manufactory or any public accommodation; and (2) any vacant land
offered for sale, lease or held for the purpose of constructing
or locating thereon any such building, structure, facility,
business concern or public accommodation.
Will your Dad be part of this lawsuit? The names of the partners get exposed, there's that as well.
My suggestion is to bend $5000 concession out of him, close the deal, and let it flow down the Schuylkill River.