When I receive a FaceTime call, my mom's iPad and iPhone both receive the call. How do you fix this?

Sounds like you're sharing an Apple ID? You ought to have separate IDs (though you can share one for purchases).

But if getting your own ID is not practical for your situation, compare her settings vs. yours under:

Settings/ FaceTime/ You can be reached by FaceTime at ...

Then select different contact points between your iPhone and her devices. Do the same for iMessage settings too.

The best solution is to use separate Apple IDs.

If you don't wish to do that, go into Settings>Facetime on the other 2 devices and only check the email address associated with the account.

~Lyssa

OK, did you check this on all devices?

Settings/ FaceTime/ You can be reached by FaceTime at ...

You must be sharing at least one e-mail as a point of contact.