With the amount of cynicism he has it'd be hard to place him in any house, bravery he might have, but not typically Gryffindor. Grades he didn't particularly care about so
Ravenclaw's probably out unless he just doesn't care to do the work yet likes to learn. I somehow doubt he'd fit in Hufflepuff, but hard work I'd imagine is something he's used to, loyalty is not though. Cunning to get his relatives to back off, ambitious, as you stated, is doubtful so write the house names down on a scrap of paper stick them in a cap and pull one out.
Interesting story I like the plot so far.