I have searched complete internet about video doorbell device that can, on easy way, support multi tenants’ buildings - no way to find something like this but looks “easy” to make it.
External unit: video doorbell with keypad. Keypad is used to dial apartment number. Should have relay to open door.
Application settings: each tenant set own apartment number in app.
Application: Video call with “unlock” button on screen.
Guest perspective: Dial apartment number and press dial.
Host perspective: Video call, answer, talk/see and unlock or hang up.
This is something easy, knowing what kind of complex technology you made. Again, it will look like one more case where big companies take lot of money for something which should be simple.