Seems like the team is going nowhere right now and if it continues a significant trade is needed. It would be nice to know if the defensive scheme is the problem or if it is the players effort. Given that, why not take a flyer on one or two experimental lineups just to see how they do.
According to 82games, the best defensive lineups are:
McCollum-Turner-Crabbe-Vonleh-Davis
McCollum-Turner-Crabbe-Harkless-Davis
Notice that both have CJ and Turner as the guards with Crabbe as SF. It looks like there is not enough data on if Crabbe or Harkless would be better here, but let's go with Crabbe. There is also little or no data with CJ, Turner, Crabbe, Aminu and ____.
Internal politics and turmoil aside, how about:
PG: Turner
SG: CJ
SF: Crabbe
PF: Aminu/Vonleh
C: Davis (or Leonard if he can ever find his shot) (would love to swap in Okafor or Noel here, each for different reasons)
Bench: Dame; Harkless; Leonard; Plumlee (he's likely gone)
If this group delivers good defensive results, then you know it isn't the team defense as much as Dame and CJ being in the back court together (which the data concludes already). If this group does not defend as well then you know it is a scheme issue.
It would also be a better fit for Turner. If you want you can swap CJ with Dame, but the data shows that Dame/Turner back court is not nearly as good defensively. Of course if the suggested lineup does work then we may see Dame Dollar turn into Dame Holler.