That sounds like a nice little game 😉
I think to make this work, you would have to put the focus of each trilogy on one character and cut everything else.
The PT-part would obviously focus on Anakin. Any PT-edit should work as a basis. If you want something more drastically you could cut down ROTS to a condensed 40 minute-movie and ad glimpses of AOTC to the beginning (something similar to the prologue in Lord of the Rings).
The OT-part should be about Luke and have only one Deathstar (change the ANH design with the unfinished one from ROTJ). I would cut the whole opening of ANH (everything happening on the Tantive IV and in the desert), until we meet Luke for the first time. (hell, maybe start Lukes arc with him being attacked by the Tusken-Raiders. Then I would continue with the original story, until they escape the Deathstar and cut straight to the battle of Hoth (obviously Luke would not be a leader of the Renegade-squadron). Ben’s “Luke, trust the Force” moment could be reinserted in the escape from the Deathstar, when they were attacked by the Tie-Fighters. The scene in which Obi-Wan tells Luke to go to Dagobah could maybe placed during the Battle of Hoth, after Lukes speeder crashed.
After the Battle of Hoth Luke visits Yoda and the plot surrounding Han, Leia, Chewie and 3PO would be cut or heavily trimmed down to its essence (maybe keep the emperor-hologramm scene). The whole Han being put in carbonite, would be cut. I would use the Scene of Lando visiting the crew in their cell and change Lando’s dialogue (unsure how), to imply that he is offering to help them escape. Then the escape sequence would play out (imply that Han is to weak to fight, because of the torture). After they escaped Cloud City, Luke will get his new hand, visit Dagobah and build his new lightsaber (use the deleted scene and add some plants to the cave). After this ROTJ would continue as usual, but without most of the Ewok and space battle part.
The ST-part may be the most difficult to think about in terms of restructuring the plot, because TROS doesn’t exist yet. Depending on this movie, this part should focus on either Ben or Rey (or both, who knows). So just cut out everything that does not support the story of them in any way.