If you create a third admin you can copy the inbuilt and undeletable and usually hidden profile to the one you intend to use. Then delete the third admin account. It main purpose from this point on is an emergency profile. User profiles do currupt. If you only have one admin account then the computer is now useless. See Copy Profile in help.
It depends on what you entered and where. Generally all admins are equal but if you assigned specific priveledges to a user (admin 1) then admin 2 won't have access unless admins generally have access. Usually no or only minor. But admins have a special power, they can take control of anything, even if they don't have permissions. See Taking Ownership in help. Note ownership changes so you can't spy on people, they know you've peeked.
Try to configure security to to use groups not individuals.
The inbuilt, undeletable admin account can be disabled or renamed. See Local Security Policy in Help.
See also
Type in Start Run
control userpasswords2 (the domain user applet rather than the pretty one)