[jrowley]

I would definitely layout all the options for the client, including an option which is abandoning your software and migrating to / developing a new option. Putting that other option on the table will make whatever you propose seem like the obvious choice.

[japhyr]

Yes, one way to look at this to get out of the "for family" mindset you've been in is to ask what it would cost them to hire a new developer or firm to build them a replacement, and maintain it. That should guide you in deciding how much to charge, if you want to continue working with them.

I imagine you are also asking yourself if you want this ongoing work. If you don't need or want the work, maybe you can agree on a scope of work to help pass the work off to another developer or firm.

I haven't been in your shoes with family before, but I have done low-cost and pro-bono work for nonprofits in the past. Fortunately those projects all wrapped up with a reasonable outcome, and no need for long-term maintenance. It's expensive to pass off projects to developers and firms that don't have an altruistic interest in a project.