Multiple castsequences with the same spell as the next spell, will all advance together.
It's been that way forever.

You can do the reverse comma's to land one spell on the team.

/castsequence [Target=ToonA] reset=5 ,,,,,,,,,,,,Rejuvenation,Null
/castsequence [Target=ToonB] reset=5 ,,,,,,,,,Rejuvenation,Null
/castsequence [Target=ToonC] reset=5 ,,,,,,Rejuvenation,Null
/castsequence [Target=ToonD] reset=5 ,,,Rejuvenation,Null
/castsequence [Target=ToonE] reset=5 Rejuvenation,Null

Could probably do more commas and make them a true sequence per toon.
That, or make one for each HOT effect (spamming until everyone has the HoT up), one button to spam for LB, another for Rejuv and another for Reg.