These are over sized pillows. I have a hard time fitting them in any of our pillow cases.
Very easy to take out some of the stuffing. Just zip the cover open and remove what you don’t want or need to make them fit or for comfort 
You can take off the cover, but the inner pillow doesn’t have a zip. You have to undo the stitching to get at the actual inner material. Not extremely difficult, but it requires sewing the pillow back up.