I'll put new rotations in the comments

76ers:

Trade: Ben Simmons, Shake Milton, and Pick 28 for Jaylen Brown and Tristan Thompson:

Sign: Danny Green, Furkan Korkmaz, Dwight Howard, Nic Batum (MLE)

They do the obvious and trade Ben Simmons. Doing this allows them to start both Tyrese Maxey and Matisse Thybulle, whose skillsets are both minimized when sharing the floor with Big Ben. They gett back Jaylen Brown, who's a great two-way player at the SF position.

Celtics:

Trade: Jaylen Brown, Tristan Thompson, Marcus Smart, Moses Brown, and Romeo Langford for Malcolm Brogdon and Ben Simmons

Sign: Evan Fournier, Paul Millsap (MLE)

Trading for Ben may seem stupid, but Jayson Tatum and Jaylen Brown do not play off each other. In essence, the lack of playmaking on the team, particularly from their duo, minimized the effectiveness of each player on the roster. Adding Brogdon as their primary playmaker (+ a great scorer) and Simmons as the secondary playmaker definitely helps. Additionally, their defense gets much better with Ben, which is good because otherwise, the defense would fall off a cliff (because Smart is good as gone).

Pacers:

Trade: Malcolm Brogdon for Romeo Langford, Moses Brown, Kevin Knox, Pick 19, and Pick 28.

The Pacers don't need a full rebuild, but they need change. trading Brogdon (who's already 28) is likely the move. Here they get 2 firsts, 3 young players to develop, and they clear up nearly $10M in salary cap (they're close to the luxury tax) so I think it's a fine trade.

Knicks:

Trade: Kevin Knox and Pick 19 for Marcus Smart

It's not a big move, but they add defense and a secondary playmaker. Thibs would fall in love with the guy.