The best possible lineup you can run with chojuro if you want to stay water with accessible ninjas is: chojuro, ao, mei (or darui). The reason is that chojuro gets boosted by water characters, so your main clone and ao clones will actually boost him (chojuro passive is wrongly translated, he doesn't boost water characters, he gets boosted by water characters, 6% per character. With the 3 clones you get a solid +42% (+36% with darui) to atk/nin as far as they survive).