I currently have the base game of Elder Sign and the Unseen Forces expansion.

I want to buy the other two remaining expansions (gates of arkham and omens of ice)

my question is:

can you combine all the expansions together to play?

If YES:

what cards needs to be taken out from the game?

also can you combine all the adventure cards and other world cards together?

If NO:

which expansion can be combined?

I currently have the base game of Elder Sign and the Unseen Forces expansion.

I want to buy the other two remaining expansions (gates of arkham and omens of ice)

my question is:

can you combine all the expansions together to play?

If YES:

what cards needs to be taken out from the game?

also can you combine all the adventure cards and other world cards together?

If NO:

which expansion can be combined?

The base game and Unseen Forces are made to be combined, as that's "Museum Mode". However, Gates of Arkham and Omens of Ice are kind of like plug-in expansions to the game engine, and they have their own mythos decks and their own location decks that completely replace the ones in the base game. From Unseen Forces, you'll still use the Cursed/Blessed cards and mechanics.

I like the system because making the expansions self-contained experiences keeps the game from getting so top heavy by piling on expansion after expansion.