Dunno how to spoiler tag so, if I recall correctly its probably Irie, Hibari and Tsuna made the arrangements, so hibari came last since he was crazy strong as it is.. and he was needed to not be worn out to kill the phantom dude. They brought larabo to trick Byakuran, and they brought the non-guardians, because Tsuna gets stronger faster when he has something to protect. 30 year old Tsuna was reluctant till the last minute to let this happen though.