@KOLDY, welcome to the forum!
As a follower, your phone does not need to be supported. I have never used supported phones and have been following my son with the regular Dexcom follow app from the beginning. There is no restriction on the follow app.
The issue only rises with your wife’s phone. When we started using the Dex I bought my son an iOS phone for that purpose. However, there is now a third party recompiled Dexcom app that has really good rep, and that runs on most, if not all, non-supported phones with good reports. I believe @docslotnick and @elver have mentioned it several times. This may be the easiest way for you to follow your wife (i.e. for her to use it)—and probably for her to be able to use her phone for her own Dexcom.
Here is a link to this thread:
That said, many people believe xDrip+ to be much superior to the original app 