Whenever I use Grand Healing it seems like my enemies are being healed as well, what is up with that!?

Grand Healing is, IIRC, made with a small area of effect. The game doesn't distinguish the difference between enemy and ally except with hostility, so whomever is within the range of the AOE of Grand Healing will be healed.

Grand Healing has a 15 foot spell radius and has the condition that it will only affect targets with a GetShouldAttack equal to 0; it should absolutely not be healing anyone hostile to you, unless they're under a magic aggression influence.

Strange, must be a bug then.

I'll point out that enemies do have access to healing spells and sometimes potions, which will produce a very similar visual effect.

That would be damn useful spell if healing spells damaged undead in TES like in some other games

I almost did this in my mod, but I found that it just ended up either making Restoration's best move in any given situation with Draugr to sit there and spam heal themselves, or (if I lowered the damage sufficiently) it was so light as to not be noticeable and not really worth a potential mod conflict.

It doesn't usually happen to me but i once got into a fight with my follower and it was healing him...
so i paralyzed him ran away and recruited him again later -not that that solves your problem-