There won't be much space for sitting up if you do that. I would suggest adding a trundle bed or drawer under the last bunk.
Thanks for your advice. The top bunk would be fine if it was moved up 4 or 5 inches. It's hard for me to recline on the lower bunk to read to my grandchildren; I wind up having to crawl out and usually hit my head. Luckily they don't spend the night that often. Lol