Upscaling a 1920x1080 video to 4K.

Hello everyone.

i should preface everything by saying I'm inexperienced in the subject, so i might be asking something that is common knowledge, but I can't figure it out.

So I have a sequence with a main video that's 1920x1080 resolution, and I have applied various edits (pictures, gifs etc) of varying resolutions as well, each with their own keyframes. I tried to upscale the entire sequence to 4K using After effects, but after the conversion, all the positions and sizes of the images were all over the place, and therefore I have to now go and retouch every single keyframe I've applied (which makes sense in hindsight, since each one was upscale in different degrees).

My question is, since we are talking about a week's worth of edits, is it possible to upscale the entire sequence without the sizes and keyframes being messed up? Maybe Nesting or some other way?

I appreciate your advice. Thank you.