How can I use screen share of my mac mini? Problems validating

I recently purchased a mac mini to act as my home media server for audio as my airport express was not playing nicely with my Peachtree DAC. Anyway, I have set up sharing on the mac mini and can't figure out how to connect from my wife's Macbook, or her iPad. (I use a PC, so would welcome advice if available on how to connect across platforms as well.) My goal is to set up the mac mini without a monitor or keyboard connected to it and have it sit with our main stereo.

I am able to connect to the mac mini via my wife's macbook IF I ask for permission and I grant it from the mac mini. However, I am unable to connect no matter what I try if I try to log in as a registered user. I have tried to add her as a user to the mac mini, I have tried to log in as a guest, and I have tried to log in with a password but no matter what I try, I get an authentication error when I try to log in as an authorized user. For more clarity, here is what I have tried:

1. Added authorized users on the mac mini. I created a user name for "jeff", "maureen", and "lastname_maureen" on the mac mini and provided a password for each user. "jeff" and "maureen" are just created on the mac mini, and "lastname_maureen" is the user name of my wife's computer. I confirmed the passwords, and still am unable to connect. I have allowed any user on the network to access screen share, and no matter what I do I get an authentication error. Again, if I attempt to log in from my wife's computer by asking permission, it works fine but I can't figure out how to set up an account to login. Please help. Thanks!