Buxton's a lifer with the Twins.
Wallner and Larnach aren't untouchable and perhaps one of them could be packaged with prospects to bring back a starting pitcher that could slot in behind Ryan-Paddack-Ober...but I'd be surprised if the Twins went that route.
Castro has his flaws but his versatility is a must-have when you consider the injury histories of Buxton, Correa, and Lewis. Other than 1B and C, there's no where that Willi can't play.
Keirsey and McCusker, IYAM, are AAA+ players and if they're traded, they'll be nothing more than lottery tickets for another team and they're not moving the needle if the Twins are trying to acquire MLB ready talent. Austin Martin's close to being in the same category so not sure what value he could bring back.
Keaschall is an IF, or at least appears to be, and for now, should be untouchable.
That leaves Jenkins, Rodriguez, Gonzalez and Winokur and I'd be shocked if the Twins traded any of them this summer.