The first frame holds the initial position of an object (i.e. prop or character).
If you delete the first frame then the objects will move to the next Transform position they were moved to or will revert back to the initial (0,0) position if none.
The thing to do before you delete any frames is first ungroup any of the pre-defined motions for each character.
Then for EACH object on the stage, in the frame just after the last one to be deleted:
1) Create a key on the Transform track, and
2) Create an Absolute key using the Motion Key Editor
Then you should be able to delete the frames (using Project Collect Clip) without the characters and props moving about.
See my CTA Tutorials on the YouTube channel CTAStepByStep
Check out EZColors for CTA. The easy way to change Render Styled (RS) colors.