I played prot warrior/holy paladin/destro warlock a while ago. This was up to around level 34 in scarlet monestary, pre 2.0. Made the paladin protection, replaced the warrior with a restro druid, and had many happy days. With the new changes to warriors it seems like they're a lot better off than before, but paladins still look to be better tanks for boxers. So basically my guess is it'll work, but you're probably better off with the paladin tank.

Also, unless you're your sibling's legal guardian, what you're doing isn't allowed.