You definitely have to take the bull by the horns so to speak. But also, your wife has to be supportive of you. I know she wants to protect her mom, but she also has to back you up in having your marriage be a priority.
This sounds crazy, but in a way I'm kind of jealous. I would love to have in-laws, or to have my husband have in-laws!
My mom died when I was 14, and my husband's mom died when he was in college. His dad died before we were married, so I never met them. My step-dad is living, about 800 miles away, as is a half-brother. I visit them once a year, but we are not close. I would love to have a family. I know it would be grief and anger at times, but I would do anything to have my mom around. I don't know if that helps you keep it in perspective or not, but I thought I would throw that out there.