Two apple watches paired with one phone

Use more than one Apple Watch with your iPhone

1. Open the Apple Watch app on your iPhone and tap the My Watch tab.
2. Tap your watch at the top of the screen.
3. Tap Pair New Watch.
4. Follow the steps to pair your new watch and iPhone. You can set up your watch as new or use a backup of your other watch.

See if this link is better .....https://support.apple.com/en-us/HT205792

Hopefully, somebody can provide a little more specifics to two apple watches paired with one phone as my mother in-law and father in-law are getting up in age. My mother in-law currently has a iPhone 7 while my father in-law does not have a phone due to him having Alzheimer's and his cognitive limitations not allowing him to use it. There is great value in both wearing Apple Watch 5's; for both potentially falling or my father in-law potentially wondering away and getting lost. Here is the dilemma; can two Watch 5's, one for my mother in-law and one for my father in-law, be used together on my mother in-law's iPhone? If not and my father in-law needs a separate phone, it will sit in a drawer and only be utilized for setting up a separate Watch 5. I'm afraid they would not get go through with the purchase if they must keep two phones on contract just to use two watches. They are on US Cellular, too.