What Ewu said. Keep in mind that there are many volunteer friends/family/couples that do volunteer and get assigned to jobs together.
Hello! I'm staff, so my brother wants to volunteer and possibly wants to help my committee out. Do I just go with him to Volunteer and request that for him? He's also underaged and is aware about his waiver form.
Is there also a maximum number of hours worked in a single day, especially for Thursday and Monday when they count for double? I.e. If my brother works 5 hours Thurs and 5 hours Monday, then that's a total of 10 hours for 20 hours worth, due to double time?
Thank you 
I do believe he has to be there personally, you cannot sign him up for volunteering when he is not there... He also has to have a paid membership, as well.
But what I think you're trying to say is if you can request Volunteers to have him volunteer for your department in which case, he can request it, or you can. He can just simply state his reason why, and I'm sure they'd understand. I do believe that your department would need to express a need for volunteers though...
To my knowledge, there is no maximum number of hours worked in a single day. And yes, if you do work Thursday and Monday, the hours are indeed doubled.
A FAQ is provided here:
http://www.fanime.com/community/volunteers/I'm not volunteer staff so I can't speak for them, so /disclaimer haha.