That is unlikely to work. They likely signed their copies or will sign as soon as you point out the missing signatures. And, they will testify they agree to it. Their signature is needed for you to ENFORCE the agreement against them not to ENFORCE it against you. You can be sure if they present the documents to a Court, they WILL be signed.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.