Several earlier posts said these guys don't help each other. Take that with a big grain of salt, my experience (lvl 58 barbarian shammy) was quite different, even when they conned grey, i had 3 on me at one time after my pet got the attention of one of them.
They are once you kit level 45. Dont worry about them ganging up on you. Your pet can be surrounded and they wont help out each other at all. Havent gotten a spell to drop from a commander yet though.
NASTY little things! I tried to solo, fear kite one of them last night... Parked my pet near the ruins, had my undead line up, pulled with darkness (Necro) and he stayed away from my pet and tried to nuke me from a distance... I ran out of range for the spell and told my pet to go get him... Being only 43, I didn't have my newer 44 pet yet. Feared and he ran away towards the middle of the zone, YUCK! Terrible pathing... Ran around the ruin to try and fear again - rut roo, darkness faded as my fear landed. And you all know what that means! Either A) my pet finishes him off or B) ZONE TIME... could FD too but wouldn't completely clear the aggro and that could get nasty or a nasty train.
Careful when fear kiting these. I would suggest if you do, to nuke nuke nuke before they have a chance to get too far out.
Solo'd these for several hours w/ my cleric...still great exp at lvl 49. Just make sure you have all buffs up, as well as cr/fr/mr buffs. Since they're wizards, keeping them stunned is the key. I pull w/ Banish undead, and they'll nuke you right away. Then stun, nuke, stun, nuke, wash, rinse, repeat. Most of the battle takes place at melee range, but they will only hit you a time or two, then stop to cast a spell. At which point, you stun, and follow up w/ a banish. Nuked me for 250 max (I partially/fully resisted their nukes 90% of the time). But when they death march, make sure you finish them off, because they will gate.
In additon to casting various nukes, they also like to dispell you. So if you are a puller or a kiter, be sure you have sow ready to recast. Good thing i have my black fur boots to instanly recast sow again.
Sorry didn't put any text. Spectral Keepers are easy kills for large race Melee. All you have to do is keep bashing. Keepers love to cast powerful slow casting Wizzy spells and do not melee while doing so. Three or more large race melee classes can kill keepers all day long with little no down time for good exp on problem is when a Spectral commader or champion spawns instead of a keeper. but they can be avoided or handled if the group is high enough level (although with much greater down time)
I have killed keepers, champions and commanders all day, and we got a few words, runes and general jewlery. Good thing is though: They don't gang up on you. We could pull two standing/floating next to eachother and they didn't help out. Low aggro radius too.
They hit for about 70 to 110, and use magic, like a shock spell with stun, firebased spell and less rare, cold based spells.