you can directly upload epubs to a kindle via
https://amazon.com/sendtokindle if they are under 200mb.
if they are over 200mb and just contain images, you can use
https://github.com/bust4cap/epub2cbz-gui to turn those into properly formatted cbz, including metadata info like chapters, then import those cbz into kcc to either turn them into split 200mb epubs to upload via the first link or into azw3, which you can then copy to your kindle via calibre (without reconverting them)