I have two questions.

Do all the cards in all deluxe/saga/single scenario expansions packages have the same backsides for the cards, like the ones from the core game?

Or do i need sleeves with the same backside for the cards, so they all look the same (of course 2 different backsides for both player deck and encounter deck) ?

All of the cards have the same backs for good (the one ring) and evil (the eye of sauron). That said there are a couple player cards and special cards from the saga quests that are shuffled into different decks than usual (treacheries in your own deck, allies played into the encounter deck), but I'm pretty sure they have the proper backs to not require opaque sleeves.

Thank you!