Family Sharing - https://support.apple.com/HT201060 - "Family Sharing makes it easy for up to six people [different Apple IDs] in your family to share each other’s iTunes, iBooks, and App Store purchases without sharing accounts. Pay for family purchases with the same credit card and approve kids’ spending right from a parent’s device. And share photos, a family calendar, and more to help keep everyone connected."
I don't know in what way he is disabled. If you fear that he may unintentionally do something that might lock you, or even he, out of his device you may wish to set Find My iPhone to your Apple ID.* I have seen an phone where this was done but specific iCloud features were set up to the actual user's iCloud account (e.g., Contacts) so some individuality was left with the phone.
Also consider using one of these:
Use Restrictions on your iPhone, iPad, and iPod touch - https://support.apple.com/HT201304 - "You can use Restrictions, also known as parental controls, to block or limit specific apps and features on your iPhone, iPad, or iPod touch, including access to explicit content in the iTunes Store."
Use Screen Time to get insights about how you use your device - "With Screen Time, you can access real-time reports about how much time you spend on your iPhone and iPad, and set limits for what you want to manage." "With Family Sharing, you can share music, movies, apps, and more with family — and it now works with Screen Time. You can view reports and adjust settings for children in your family any time, right from your device."
https://support.apple.com/HT208982
Do not forget the passcodes used to set these or you will have to wipe the phone! However, proper use of them should prevent him from accidentally.
* Should he unintentionally mess with Find My iPhone, change his Apple ID password and do something to trigger activation lock the phone will be useless to either of you.