Maybe FATE OF THE REPUBLIC could be Order 66 Origins and Siege of Mandalore instead? I wanted Ahsoka to be the main character of the final film, but her side adventure with the Martez sisters isn’t as important to the final arc as Fives’ discovery is.

If ORDER 66 ORIGINS is in the final film, the rest of the Domino Squad arcs won’t really be necessary. The opening crawl can just explain that Fives is a clone and a friend of Rex.
Also, then Ahsoka’s return in THE SIEGE OF MANDALORE would be as much of a surprise to the audience as it is to Anakin and Obi-Wan.