Hi @CZimarino,
It’s not possible to keep two HubSpot portals in sync using default HubSpot features. (There are integrations for that.) If you need both databases to be in sync, you would have to use one portal.
Personally I’d be concerned whether there are privacy implications to managing contacts belonging to two companies in one portal. You might want to check this with a legal professional.
If you’re using one portal, it doesn’t matter which email address you use for logging in. You can connect multiple email addresses for sending personal emails, as explained above: Connect your personal email
Hope this helps!