My suggestion is to set up a reasonable time line for the remaining
work. Sit down with the husband and wife and explain that due to your
family obligations you need to finish the project by a given date.
Explain after that, you will not be available and that they will need
to hire someone to finish the job. This gives them an incentive to
make the necessary decisions in a timely fashion and gives you a out
hopefully without hurting the relationship. The hard part is to call
it quits when you reach your drop dead date. You must be firm. They
should understand that you have a life too.