This is precisely the way Apple and the devs of the smart device and its app would want it handle. The admin phone (yours) has the manufacturers app, invitees don't have anything more than the Home app.
Firmware updates is a given. This is always done through the manufacturer app. But just as importantly devs will also give the ability to make scenes inside the app that can be run in the Home app that couldn't otherwise be created. Specific values for automations/scenes oftentimes are made in an app. A trigger at a certain humidity/lux/temp/etc for example, or the desired value when an automation is run like temp/humidity based on home/away.
The beauty of all that is once its set up how you want it will operate like magic for your parents and they can have basic but full control of the home.