1.  Create 2 Nexx Garage accounts

2.  Log into the first account and configure device #1

3.  Grant access to 2nd account

4.  Log out and log in as account #2, configure device #2

5.  Grant access to 1st account

Now, from any account, you can control all doors.  However, account #1 is the owner of device #1, account #2 is the owner of device #2