OKAY here's how this works. When you die and are revived later with edo, you retain all your old power including old doujutsu that you had when you died.
in the example I give in the topic I created, sasuke gives his ems to suigetsu and then kills suigetsu. sasuke removes ems and puts it back in his head. oro revives suigetsu with edo and then gives him free will: Now suigetsu has both ems and an undying body. sasuke still has ems as well so no loss there.
For the brothers example, it's pretty much the exact same. Bro 1 loses his ms so bro 2 gains ems. bro two is killed by bro one, then bro one takes bro twos eyes. then bro 1 revives bro 2 with edo and now bro 2 has edo + ems and bro 1 can see again and also has ems.
