This is an interesting concept. I'll not delve in to it as it presents difficulties, however, I'll reiterate that often young folks are doing one play, whilst adults do another, and the play that is being acted out in the lives of youth isn't always known to the adults in their lives.
That being said, I have an active mind, and contemplate scenarios all the time in these cases. So this is purely a what if....it's only conjecture....what if, one twin was unaware the other was going to commit suicide, for reasons of jealousy per se, or some other reason, and upon witnessing that event the remaining twin simply could not endure, and did the same?