1
I wish I had better news for you, this forum is just a user to user forum, for security purposes, no-one here has any account access, when a Microsoft account is hacked, if the hackers change the associated data like the Email, then that account is usually no longer recoverable, try using the process they provide on this link to recover a hacked account, if this process is not successful, sadly, that account cannot be recovered.
2
For the PC's, are you actually able to get into Windows on your PC's?
If so, open the Settings App.
Go to Accounts - Your Info.
In there, should either be the option to 'Switch to a Local Account', or the option to 'Stop automatically logging into Apps with this account'.
Select whichever of those two options exist, that will switch your user profile in Windows to a local account.
You can then add the details of your new Microsoft account to the user profile.