You can synchronize animations by setting the Speed to 0 in the Preview view, set the animations you want to play on the tracks, and then set the Speed back to 100 (the default value).
Currently, it is a bit cumbersome to do this, but we plan to make various improvements to the Preview view, and once those are implemented, it would be a bit easier to synchronize:
https://github.com/EsotericSoftware/spine-editor/issues/371
