Multiple domain email addresses to a single 365 mailbox

We have several different domains on different GSuite accounts.  Our original primary domain is on Exchange.  I recently migrated that account to Exchange 365.  Now i would like to move all the gsuite accounts to my 365 account.  the problem is that userA has a 365 mailbox and also has 2-3 gsuite mailboxes.  what i would like to do is assign the email addresses to the primary 365 user, then point the MX records to 365 so that any mail sent to that users gsuite account would route to his 365 mailbox..  not 100% sure that will work but if it does, the next question would be, how do i get each users mail from their gsuite account into their 365 mailbox.  Maintaining all these accounts across two different platforms is causing issues for users with calendars, etc.