I also tried to connect different pairs of the same brand but didn’t succeed either by using some clone apps. Probably not the right ones. Forgot which ones and I am done with it by now. (Android phone now has remnants of clone apps which ask for sign-in’s etc.) Only way to deal with two HA pairs of same brand for me was by forgetting in the settings etc. But maybe others will have good experience by some of the apps that will work for them.
At the other hand I now own a Phonak P90 and one the same kind branded Amplifon. I managed to get the ampli-energy Phonak P90 to connect with the Amplifon app and the Phonak P90 to the MyPhonak app. And I can do DIY in both with the same Target software. (By the way I like the Amplifon app far more than the MyPhonak app as it gives me more available adjustment options).