Some ideas for you and your brother:
Officer Jenny (or Nurse Joy) and Ash Ketchum from Pokemon
Taiga and Shiro from Fate/Stay Night
White Mage and Fighter from Final Fantasy (or any other combination of classes)
Kagome and Sota from Inuyasha
Elice and Marth from Fire Emblem
It's not really anime/video game related, but it would be pretty funny if he was Phineas or Ferb and you were Candace XD
If I brainstorm any more ideas, I will post those as well.
Best of luck with your costumes!