unless they are identical twins it isn't hard to tell them apart. even with identical twins their are ways to know one from the other. it would be stupid to not do both. that would be like saying you cared more for one son than the other. i say either should do both or not do both. haven't seen or read anything about this, but some people probably have done this tho. the way some people are now days, an the world we live in .. its possible its been done for this reason only. i do know one of my friends twin boys wasn't circ. when born an the other was circ. but it was because at the time her Dr.told her he didn't have enough their to cir. but her son latter had to be when he was 18 i think not sure why. but she was asking me questions an it came up that he had to be. her other son ask her why he was different than his brother i guess, when he was much younger, she explained to him and all was well apparently after words she said.