Francis' family all have different smartphones, and they are having a hard time with calls and text messages, no matter what phones they are using. They are all updated phones, all on T-Mobile, and they don't really know what to do. Leo says that the issue is likely cellphone towers and coverage in her area. Maybe a few towers are down for maintenance? Or were the towers shut down when T-Mobile merged with Sprint? Since that's when the problem started, it's likely the merger is a main culprit. It may also be time to change carriers. The good news is that you can change carriers and try it out, and modern cellphones can switch from carrier to carrier. So you wouldn't have to buy new phones.
What you can also do is tell TMobile you need a FemtoCell for your home, or you'll leave the carrier. It will then route your phone activity through your internet connection. But if WiFi calling isn't working, then that's not going to help.