The National Association of Marlon Brando Look Alikes?
North American Marlon Brando Look-Alikes?
Incest has been shown to have serious problems, greatly accentuating genetic weaknesses that show up as recessive genes. The probability of these paired recessive genes are much multiplied in sibling pairings, which has been amply demonstrated by animal breeding experience.
Of course, if the sibling pairings avoid production of live births, this objection is somewhat less strenuous. But there are still the psychological and family structure aspects to consider, if your parents are also your in-laws.
And there is the power balance between the parties involved. Who would have seduced whom, in this instance? Can abuse be claimed, if the fight turns from sibling rivalry to marital incompatibility?
It is a rat’s-nest of problems worthy of a dissertation by Marquis de Sade. Most of those conflicts were resolved by homicide of one party or the other.