Several ways....
1) add a unique keyword to your magic effect. Take a look at the Twin Souls perk implementation which uses modify commanded actor limit and implement a similar perk, but change it to use a keyword on the magic effect. In your spell, you'll need to put the magic effect in their five times.
2) More convoluted. Create a quest with 5 aliases and add the PlayerFollower package to them. Instead of summoning effect, use a script to place the npcs at the player and then add them to the alias. This is from memory, and you'll have to figure out the quest and proper referencealias for your script, etc but it can be a good learning experience.
objectreference NPC1 = Game.GetPlayer().PlaceAtme(NPCActorRef)QuestAlias1.ForceRefTo(NPC1); rinse and repeate 4 more times for each NPC
At the end of the effect, disable and delete the NPCs.
-MM