FaceTime problem on iPhone 5/5C iOS 10.

The FaceTime problem does not just occur on only one iPhone 5, it also happened on the iPhone 5C, and another iPhone 5, but FaceTime works for the iPhone 4/4S. I don't understand why because I logged in to iCloud and did everything with all these phones, but how come FaceTime didn't work on my iPhone 5 and 5C? It worked on my iPhone 8 and iPad Pro somehow, even my iMac. I tried connecting it and it is stuck at waiting for activation, then it won't let me continue. Here are pictures proving it.

I didn't make it up, and didn't close it, it was stuck and I couldn't bypass it. I really want to interact with some of my employees using my iPhone 5, not my iPhone 8 because I use it for something else, and not the 4S because the camera on the 4S is 0.3 MP (VGA).