1. Welcome to the forums!
2. Do not sell. The drop off if any will be minimal.
3. I guess you could sell if you're getting pieces like Eichel and Karlsson back.
4. The duo underperformed last season, so I am actually thinking that if they go either direction, it will be up.
Basically what I'm trying to say is don't worry. That will lead you to overreact, sell low, and spend a long time regretting dealing two of the best talents in the game.
You do however have a lot of one dimensional players. I would suggest moving one of Kuch, Kuz or Kane for someone to diversify your stats. I would target Eichel and Karlsson first of the names you mentioned.
How many teams are in your league?