We should not giving up 1sts at deadline, I think we will be sellers

Zero chance Carter waives from Pittsburgh where he's stated he wants to raise his family to the heaviest tax burden jurisdiction in the NHL.

That barely enough to dump Carter

With the move Dubas has made, I cannot see them selling. They already moved a first to get Karlsson. I think they have to go for it

I hear you, but I just don't see how we can be buyers if we continue playing the way we are. If we're 5-10 points out of playoffs and continue playing poorly I don't think it's a good idea to throw away another 1st. Dubas also said in an interview the next two games (before lightning game) will determine what he does. And I remember in his press conference he said you need to be able to adjust strategies if the team goes off track and is out of contention. I just can't imagine this team competing for another cup. I hope I'm wrong.

Or you make trades early enough to have an impact on getting into the playoffs. Risky, but Pittsburgh is at the tail end before the inevitable rebuild. If you're not all in, might as well start the post Crosby era now.

As for the trade, a little light to trigger an early move with retention. An extra conditional pick may do it. The value has to be definitively higher than what it "might" be at the deadline. Right now it "might" already be a 1st, so there's no reason to accept Carter or retain to make it happen early.
That's assuming Carter waives, which I don't believe will happen.

Ignoring what Montreal would receive, I think Monahan would be a good fit if Pittsburgh can figure it out.

I don't think there's one fix for the team. There's so many issues (lack of speed, no net front presence, bad team defense, no toughness, system that doesn't work anymore, etc.) Given that I think it's probably best to start the rebuild.