I romanced Shadowheart pretty successfully with a Paladin in good standing (Oath of the Ancients). In an earlier run through my Wizard was doing OK with her too, but I ultimately gave up on that party.
I don't think you could convince me to romance Astarion or even Gale, lol. Both of them have an off-putting arrogance.
I don't really want to work hard enough to get through Lae'zel's shell. I think I would start with a Githyanki character though.