Contingency plans

If a contingency plan is only signed by one spouse and not both is it still legal and binding?

Depends on the jurisdiction.

In the dfw area of Texas…

Is the contingency plan part of the primary contract or an addendum after the fact? If it was part of the contract, then the signing party/parties would have accepted it as such as part of the whole original agreement. If it is an addendum to the contract attempting to indemnify a party not signing the original agreement to which it pertains, then I can see that being a problem.

The contingency plan, in the form I assume you are meaning, is nothing more than another contract. Am I incorrect?

Would it not be easier to get signatures on “change orders” prior to embarking on tasks outside the original scope of work which might trigger additional expenses?

The homeowners are no longer wanting to continue services with the contractor anymore.

And what is your part in this mix?