Itachi didn't take his dad's eyes because his dad did not have Mangekyo Sharingan. to get EMS you must transplant eyes that have MS. also, i don't believe it must necessarily be brothers but yes it is more likely to work when you take the eyes of a sibling (though i think anyone in your immediate family may work, i still think a sibling would be ideal). Also, I truly believe that Itachi never wanted EMS because to him it was a curse--murdering a friend to get MS and stealing the eyes of a family member.
Somewhere it said that it's been tested over and over throughout the generations, but it works best with siblings. And his dad would have needed to have a mangeckyou himself. Why he didn't transplant shisui's eye though is beyond me.
i agree about the closer relations but again I just think Itachi never wanted EMS. as for why he didn't transplant Shisui's eye, that wouldn't have made sense. First of all, he would have two different eyes--one of his own and then Shisui's. so while he'd have KA, he'd lose either Amaterasu or Tsukiyomi depending on which of his own eyes he took out. also, if it worked and gave him EMS, he'd only have EMS in one eye which would just be weird. i think his idea of keeping it in a crow was a good one. that way, he had both of his eyes AND Shisui's KA. so he had 3 eyes with MS rather than just 2.
Good point.
I don't think that you have to have blood relation. Danzo is clear example.
not sure what you mean. Danzo did not have EMS at all. he simply transplated a bunch of eyes, which was only possible because he also implanted Hashirama's DNA. but yeah, Danzo didn't have EMS
