Forced To Provide Intellectual Property Before Payment Or Contract.

I am keeping this brief to protect myself.

A relative tricked me into creating an artistic property for them to sell. It began with the relative hinting that they needed a design for something. I sketched up some ideas, thinking that would be the end of it, only for them to demand I confirm and polish the product. They told me they would pay for the license to use, but it wouldn't be upfront.

I felt uneasy and stated I didn't want a part in it. They then physically threatened me and demanded I do so. I finished the product against my will, which they have been selling since. They demanded access to the product before payment or signing a license due to "time constraints." A year later, I have only received half of the payment. The license is a standard template that proves intent to fulfill payment and consent to use.

Everything we had verbally agreed to is in that contract. They now refuse to sign it, portraying me as "shady" and stating that, because we are related, they shouldn't have to sign anything. I explained that the court doesn't recognize word of mouth and that we needed legal evidence of the exchange—that they wouldn't be obligated to send a cease-and-desist to others for using the design, as they don't have documented proof of usage rights. They still won't sign it.

I'm uncertain how to progress. Can a contract even be viable under threat? They forced me to hand over the property and now refuse to sign the license or complete payment within a reasonable time. As it stands, they don't have legal rights to the work, and this was something I never wanted to do.

Is there anything that would force them to sign it? Or do I have to send a cease-and-desist for them selling the product outside of legal documentation? I fear doing so would risk my safety. I've considered sending an email stating that their continued use of the product is an implicit agreement to fulfill payment and abide by the terms I will list (Such as not involving me in printing/shipping, handling infringement, compensating for damaged products, etc.) Would that be legally acknowledged? I fear them using my name for things I don't consent to.

Location: TX