dim version? amplify damage ? decrepify ? try changing to a holy freeze merc and slow those ancients down ? keep recasting clay golem on top of one of the ancients to keep at least one occupied then run to the opposite side and hope your skeletons follow you and focus on a different ancient
keep trying to divide and conquer
make sure your merc has a lots of life leech and crushing blow ?
You will probably want to use Decrepify, and possibly Life Tap if/when your merc gets low. Also, feed him lots of potions. If I am playing on an underpowered character, I will buy a lot of potions, and scatter them around the Arreat Plateau so I can pick them up throughout the fight.
I know for Act bosses, Clay Golem has a high attack priority, so you can try spamming Clay Golem on top of the Ancients so it can soak damage.
You can also reroll them by opening a Town Portal if they spawn with bad mods (ie, cursed, fanatacism, etc).
Urgh.. skeleton mages. Nevertheless, as everyone else has said I'd do decrep and alternate with Life Tap to TRY and keep merc up. You could try starting off with a cheapass Iron Golem just for some petty damage return. When he goes down, which will probably be pretty fast, spam Clay Golem. What revives are you using? I would go to A4 and get Urduars. Combine that with a teleport item and rerolling ancients it shouldn't be too hard.