A reformed thief decides to help his reclusive brother, court his dream girl, when he discovers she’s the daughter of a wealthy investment banker.

The conflict would be much higher if he's perhaps not a very good thief, in debt to some gangsters, needs one big score ... and then this falls into his lap? Maybe his brother is already thinking about asking the girl to marry him ... and suddenly your protag needs to seduce the girl to get to her father's cash?

You should specify 1) what type of thief the brother is 2) which brother is after the dream girl 3) where is the hurdle to overcome.

I don't see a "likable" character here. Who am I rooting for?