Welcome to TTF.
You can run many units from Home on the computer. The key thing is that each requires a separate account set up with a different email address (it doesn't even have to be a real email address, just in the format of (e-mail address removed).
So, you have one model connected to Home with an email address/password (look for the email address to appear in the top right of the screen and the model in the bottom right of the screen)
If, after a few seconds, it is not showing the email address associated with unit 1 when you created the account at TomTom, then use the log in link to type in the email address/password.
When you are through doing whatever you want to do with the first unit, disconnect properly from Home using the Device disconnect icon on the bottom right.
Now, connect unit 2 to the computer. Home sees this as a second device and basically says it doesn't have a linked email account associated with this new device, do you want to create one? This is where you put in the 2nd email address/ password and this combo will be associated with unit 2, whenever you connect unit 2 to Home.
Bottom line: each unit needs its own email addressfor Home to keep it straight.
I have four separate units here, each with its own email address association. Home works fine, recognizing each as a different unit.