Well, they certainly reinforce the blood feaud that has been going on for generations. In act 1 both old men (Montague and Capulet) are out with their swords. This sets the stage for our star crossed lovers and the whole forbidden fruit attraction. Both R and J feel their love is doomed because they are bound by the ancient tribal customs perpetuated by their parents. So yes, to an extent the parents validate the extent both R and J go to. THe Friar too aids this theme with half baked schemes to bring both families together. Add to this impulsive youth, blinding love......and you have a great tragedy.