My son's mother and I own a house as tenants in common with right of survivorship. I do not live with them but we still have a strong relationship and do a lot of things together. She contracted with a company to do work on a remodel and I am not a party to that contract. There is now a dispute with that contractor who has filed a mechanics lien and things are getting ugly. I never signed this contract for the work. Does that make the contract void or voidable?
The simple answer is no: the contract is not void nor is it voidable on the stated grounds.
California does not recognize title to property designated as “tenants in common with right of survivorship” Are you sure you got this off the deed? If that is on the deed you are tenants in common with no right of survivorship under California law. If the deed says something else, it could alter the analysis.
In general either tenant in common can contract for work. The other tenants in common are not responsible for the payments, unless they signed the contract. However the entire property can still be subject to a valid mechanics lien. If a sale is required to pay the lien, only the portion of the pro rata share of the tenant who signed the contract can be used to pay the lien.