This is an important problem for sure. With as of yet no clear solution.

Because of the one time per macro limit of /targetenemy its clear you have to press the key a number of times.

Put a /targetenemy on the main and you will cycle though.

Put /assist on the followers and they will also cycle though.

Then stagger the casts on each follower,

/castsequence LB,,,,,
/castsequence ,LB,,,,
/castsequence ,,LB,,,,


Would be nice to see better alternate solutions.
Use a Pal and consecrate ... lol.
What about thunderstrike doesnt that do aoe damage?