Who should Houston be willing to give up, or NOT give up?

First off, for a relief pitcher, the Astros should not give up a top prospect like Kyle Tucker or Francis Martes. Those guys should be off the block.
With Alex Bregman, Yulieski Gurriel and Marwin Gonzalez‘ ability to play the hot corner, third base prospects should be easily expendable. Colin Moran is batting .300 with 17 HR’s in Fresno and is a former 1st Round pick. He should be a prime target for rebuilding teams and is big league ready. J.D. Davis could also be a valued trade chip as he is rocketing through the minors. He currently is in AA Corpus Christi and is hitting .288 with 19 HRs.
OF Derek Fisher has enjoyed success in Fresno and his short stint with the Astros earlier this season. He could be a part of the Astros future very soon, but with a player like Kyle Tucker waiting in the wings, Fisher’s departure could be worth more than him staying. His value is peaking due to his big league performance this year.
2B Tony Kemp is batting .331 with 14 SB’s this season in Fresno. He, like Moran, should be playing in the Majors, but the Astros are simply flooded with talent at present. He should be a part of a trade.
Other players like Preston Tucker, A.J. Reed, Tyler White, and Teoscar Hernandez should all be on the block, but their values likely aren’t as high as they once were.
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A combination of a few of these players for one of the relievers listed above should seal the deal and give the Houston bullpen a needed boost.
***Stats per Baseball-Reference & Fangraphs***