Insane Difficulty: Help me with WoR please - Insane Difficulty

I'm looking for cloud , i just can't find him , also when you het odin is there a secret passage to get the 2nd odin version like in vanilla ?

There's an NPC in the Tyrano Tower entrance that once you give him lots of Gil will give you a Magicite as well as a hint to find Cloud, or rather the entrance to the Phoenix Cave. Something about a "humanoid looking mountain" that you need to find, and land on what would be the head.

There is a switch still for that area of the Ancient Castle. It's just been moved to another spot in the room. There's a direct hint for that if you got the Ancient Letter Rare item, which is what the Emperor's Letter was in vanilla game. If you get that it tells the pattern of steps to take to find the switch.

And about the doors sealed on fraust cloud doesn't unlock them just like Lock ? any clue where i can open those doors

You'll need the Heartless character to do that. He replaces Umaro.

I'm I supose to bring a specific char ? cuz , he say [...] with my current party

Ah as was the original, you need to bring Mog.