I'd pass. Generally, when you give 2 players to get 3 players, you're getting the worse end of the deal. Even so, I still don't like the deal. Ramirez seems to be hurt a lot. I do like Morales, but Niemann is sort of... meh for what you're giving. Remember, you'd have to drop a player if you were to accept this deal. Pass.
Definitely don't let Felix go, especially now that's fulfilling his potential. It doesn't make a difference here but if this were a high amount of keepers, I could see the consideration but if it's a low amount, like 5 guys, not even worth a glance to me, don't let Felix get away.
this is a terrible deal. in a league where all keepers cost the same amount, i wouldn't be keeping a single one of the guys you're getting back. MAYBE aramis, but that's it. Felix is worth much more than all 3 guys you're getting. then you're throwing in vlad (who's heating up) for nothing.
The only two big keepers I see are King Felix (keeper in a league which you keep 2 players, potentially) and Kendry Morales (further down the line, but keepable).