ToME: the Tales of Maj'Eyal

I'm level 16 and the boss fight against the Chronolith Twin and Clone seems absolutely impossible and bullshit on multiple levels. The previous areas in the Rift were not easy, but perfectly beatable, and I've seen the bosses beaten with other classes at a lower level. However, with a Bulwark it seems there is literally nothing I can do. I can't fight around a corner because they stun me and then teleport me into the water, I can't separate them because they just destroy all the trees around me and expose me to the other boss... how the hell am I supposed to deal with them?

Your first issue: you're level 16. Most people save Daikara for levels 20 or 19.
Second issue: most melee characters ignore the rift or save it for a much higher level due to the bosses and the first stage, where movement takes 3 turns.

As for dealing with them, I would just say hide in the corner you spawned in and pray they don't teleport you. If they do, run like hell.

I typically walk through the rift on returning to Daikara for the backup boss, and it's a walk in the park, mostly....

Don't waste time trying to separate them, they tend to do that themselves when rushed.

Anyway, I decided to screw the rules and just savescum the fight and finally managed to kill them on the run after the one that prompted this thread. At least now I know not to use the Rift until I'm much higher level on my next character.

My biggest problem with the whole thing is that apart from the bosses, the previous three areas (even the first one with the elementals) are perfectly beatable at level 16 with tactical use of Rush and resting up after each group of enemies, so the Twins come as a completely unexpected (and unavoidable, unlike overleveled elite monsters in other areas) difficulty spike.

I usually dig a zig-zag tunnel heading right into the trees near the entrance so I have somewhere to fall back, then spend the early part of the fight poking my head out of the entrance, throwing out a ranged attack or two if I have one, then retreating back in to heal. Once they begin to seperate themselves is when I'll start the fight for real.