I don't think it would be too over-powered. Spirits are pretty dumb anyways (in fact I would prefer better AI than this but...) if each Rit could have just 1 of each type, it wouldn't be so bad.
The global effects could be made to not stack.
Recuperation:
Whether you have 1 or 5 you still only get a max of +3 regen. That sort of thing.
Shelter/Union/Displacement etc.:
All 5 Shelter spirits lose hp when they prevent someone taking more than 10% damage. Similar deal for the rest of them.
The Attack dudes:
This is the main point here. The fact is spirits are already stupid. If you have 1 target, sure, that dude is as dead as a door-nail with an army of spirits

(not much different to a minion army). If you have more than 1 target then the jury is out on it. They are quite vulnerable since they can't move anywhere. An AOE from an ele would do the job pretty quick.
To balance it out a bit, perhaps all the attacking spirits should have less hp than they do now, making them even easier to drop. Or maybe even (the Rits are gonna' hate this but) within range, when one Spirit of Pain takes damage, they all do.
How would that do for balance?