I wouldn't know how. If they are accepting that may help, but if you're young with homo/transphobic parents I do NOT recommend coming out and asking if you can wear certain clothing they wont approve of
Well, if you can't convince your parents to wear an actual crop top you could always just tie up a t-shirt or button down into a knot after you leave the house and undo it before you come home. Bam, undercover crop top. 😉