The only way I can get this to work, without incorporating delays, is to use different ranks of the spell:

(1) /castsequence [target=Aaa] reset=5 Rejuvenation(Rank 15),,,,,,,,
(2) /castsequence [target=Bbb] reset=5 Rejuvenation(Rank 14),,,,,,,,
(3) /castsequence [target=Ccc] reset=5 Rejuvenation(Rank 13),,,,,,,,
(4) /castsequence [target=Ddd] reset=5 Rejuvenation(Rank 12),,,,,,,,
(5) /castsequence [target=Eee] reset=5 Rejuvenation(Rank 11),,,,,,,,

If they're all the same rank, then it will progress the other castsequence. If they're all different, then it works as intended... very frustrating!