There is a simple way to resolve the dilemma as to whether PM Lee should sue his siblings, without getting all conflicted or writing a thesis. PM Lee can sue LHY and LWL for defamation and seek nominal damages. That way, he can preserve his reputation and that of his office, and show that he doesn’t practice double standards when his character and integrity are impugned.
He will also, in only seeking nominal damages, show that he only wishes to clear his name, and that he is not looking to punish his siblings or to further damage his relationship with them (if that’s even possible).
And most importantly, it can give the matter a proper airing before his actual accusers in a proper forum. And he will demonstrate to his critics that he has nothing to hide.