Four of the players have guaranteed contracts(Theis, Edwards, Wanamaker, Poirier) and can't be traded for months so that is a pretty easy 4 of the 5. Waters and Strus have 2-way contracts, so it's pretty easy to rule them out. Maybe and Gates are just bodies for practice during training camp and pre-season, so it's pretty easy to rule them out.
What your question should ask is who, between Tacko and Green will make the team. I want to see much more before I decide but after one game, it sure looks like Green is an NBA ready player while Tacko is extremely raw. But both were playing against absolute scrubs so not sure that helps.
Tacko's potential to be something very, very good in a couple few years is intriguing so probably have to go with him but, if Waters or Strus show they really have no NBA future, I would be okay with dropping them, signing Tacko to the 2-way contract and trying to get someone on the team that could be a possible rotation contributor. If Green shows he is that guy, great. If it's by signing or trading for someone else, that is great too. If it means leaving the roster spot open to add someone later, I am good with that too.