Sudo questions

Here's the scenario

I have user1, user2 and, of course, root. What I want is user1 to be able to sudo as user1 or root and authenticate with their account password, not user1's password or root's.

I've been through:

man sudo

and I still can't seem to find that answers. What am I missing?

If he has the passwords, can't he just su?

this link suggests the runaspw option, which you can apply to a user rather than a command in the sudoers file.