I am trying to clear the Paradice walley from titans, however I stright get killed with one shot. What protection should I have and in which level to avoid this to happen. At least not this fast

Magic Protection helps some
A point of return for Lloyds Beacon nearby
Two casters that can get to a Town Fountain
And try to get as many from behind hills or buildings by using Meteor Shower. aiming with Wizard Eye
That is how I did it.

It's much easier when you can Fly, as you can move more quickly to dodge their instant death attacks.

Problem with flying is that Titans had an uncanny ability to take out the Wizard who cast the flying spell.
When I first played I was mocked for using the up/down to avoid being hit.. Scumming it was called.
I tried to defend it as a "Z" force as in Star Trek (yes, I can be verrry nerdy) but I still avoid it.

If I have a scroll for flying or feather fall, than I will fly around the Titans but I know which Wizard is going to get it.

In real time mode you can fly quickly enough to easily dodge the projectiles, so even the mages should be safe while raining meteors down on them.

Enemies can move during pause time, I can move during pause time. I feel zero guilt for Z dodging!

Supreme titans can insta-kill; that is their random special effect. The answer is lots of Luck (75+ base, and buff from there) and Magic (I guess that is the one) resistance to make this a very rare event. Plus two characters who can Raise Dead followed by Shared Life and/or Power Cure.

Titans are the ultimate monsters in the game, arguably. If an ordinary one's ordinary attack is doing enough damage to kill characters in one hit, then you need to level up more before fighting them. My people were level 85 before I went to Paradise Valley, and had finished all the Oracle's story-line quests except the last one. I'd had an expert in Dark magic since level 50; going for master wasn't crucial. If it had been, I might have tried dodging past the titans in the Paradise Valley village to get to the house I wanted, instead of destroying them.

Titans ordinarily do electric damage but sometimes cast a spell for magic damage, so high resistance is needed to both. And enough health to survive the hits when resistance unluckily fails: the grunt (basic) titan's normal attack is pretty consistent, up to 100 damage a time, but its spell is highly variable, to a maximum of nearly 200. (I got those numbers from my usual website cribsheet)

I enjoyed playing the default party (PACS) with all combat turn-based (real-time movement allowed both for charging in close and for running away!). My archer (better protected than my wizard) became my flying pilot but I usually landed to fight (except against sea serpents and against dragons, when I wanted to get into point-blank fire blast/shrapmetal range, or melee). I didn't bother with exploiting the airborne dodge-up/down-in-turn-based loophole, yet destroyed every monster everywhere, titans included, so it can be done.