I believe that we can resign them, but we'd go over the cap into luxury tax territory. At that point it's a strategic decision whether keeping them is worth incurring luxury tax. I don't believe we'd keep them if KD signs.
And you're right, once we waive these guys, they won't make it to free agency. Their contracts are absolute bargains compared to today's crazy market. Teams will pick them up on waivers to get 1 year of bargain priced play and worry about the market next year when the cap goes up again.
If Jerebko would sign for the room exception that would be great. Otherwise maybe we'd go for someone like Crawford who might take less to play with a contender?
After Durant, we wouldn't have any real cap space to sign them with. Pretty much you'll only have the Room Exception, and that would certainly be good enough for only one of them.
I could see Jerebko actually accepting the vet minimum
I'll say this though, if Amir and Jerebko are waived, which we'll need to do regardless to get Durant, there's no way some other team doesn't claim Amir and Jerebko. They won't be free-agents this year no matter the scenario, I can pretty much guarantee it.