1) Celtics get Poeltl
Celtics get Poeltl with the idea to sign him by trading Williams. Since Williams wants an overpay and has priced him out of the Celtics plans, get Poeltl who provides the security if Timelord's health or Horford's age catches up with them. Give Poeltl the close to 15-20 million versus giving it to Grant Williams. The Celtics roll the dice that Gallinari can do some of the Grant Williams things at least on offense in the playoffs and between Poeltl and Gallinari they fill the Grant Williams void. If Timelord latest injury is the new norm and Horford is already slowing down, this position is a bigger need than the Grant Williams utility role. I love Grant Williams and the flexibility he provides but hate to lose him for nothing and gamble away a bright future that could last 5 years if they Celtics can solidify the Center position.
2) Lakers get Pritchard and Williams
This changes the Lakers completely to get 2 top shooters and gives them a chance to complete this year.
3) Spurs get the Lakers #1 pick in the future and any players needed for salary filler. This makes the tank this season for the Spurs complete which will help them in this year's draft too. The Spurs are going to lose Poeltl anyway and getting a potential lottery selection could turn into gold. Plus, it gives them a better shot of being bad this year and getting the top player.
All 3 teams throw in an extra player as needed for salary filler.