Herondale's:Make the girl become incredibly attracted to you. Then break her down by becoming her brother, or revealing you had a fake curse. Perhaps make her feel like shit for a while because you feel crap yourself. But all the while confusing her by having random hot make out sessions. When you find out that you're not siblings or that there is no curse, make things awkward again by becoming a servant to the girls real evil brother. Or by not avoiding the girl because she is getting married to your bestfriend. During all this the girl's love for you should only increase. Eventually everything will turn out just fine. You know, after suffering a ridiculous amount.
Lightwoods:Either order scones and hide them under your bed where they'll rot and stink up your room just to see the girl. To make the situation more awkward sate that the two of you will be married before she even knows. So you better quickly confess your feelings in a huge declaration of love. Or you could be sassy and state that the girls knife skills are a five, she will then proceed to go all sassy on your mouth and your sass filled relationship will be born.
Morgenstern:Either kidnap your x-wife and put her in a coma and try and kill her daughter a few times. Not to mention try and take over the world. Or be the evil big brother and try and rape your sister and steal her boyfriend. And also try and burn the world down. Girls like bad boys.