When you change password, it will ask for confirmation like a code, it either ask for code from mobile app you had link the account to, or code from email for the account.

Yes you can use same email for multiple steam accounts, they even same account name in the mail so you're not confused which account it is for.

No Steam does not transfer games to other accounts, so making multiple accounts isn't ideal thing to do for number of reasons such as forgetting accounts, losing track what account you were on when buying things, and etc...