The Spurs could actually end up with Mahnimi, Washington and Williams on the Toros. However, to make that happen, the Spurs would have to waive Williams. If Washington is waived there's a pretty decent shot he ends up with an NBA team. Even if he doesn't, he'll either get a big offer from Europe or he'd be picked high in the NBDL draft.
Williams, on the other hand, could be waived and then if he enters the NBDL, I'd say there is a really good chance the Spurs/Toros can pick him ... if they still wanted him.