Euthanizing isn’t the answer to your issue. Our site has a lot of information to guide you through treating it. If you’re unable to treat your chickens, I strongly suggest seeking out people who are willing to take them and treat them. Bumble foot is painful, and your birds can ultimately become lame and die without treatment. Since the ground they’re being kept on seems to be a major issue, you should consider changing it to make it more forgiving on your chickens feet. Make sure anything they can cut their feet on is removed (sticks, sharp rocks, metal). If it’s too rocky, then add dirt and/or shavings. I’m not trying to be critical of your chicken-keeping. I’m only trying to give you options to avoid what you're planning to do with your injured chickens. If you can’t treat them, you can find someone willing to. Then, focus on doing something about the area that the remaining chickens are walking on in order to avoid more injuries. I wish you well, and I hope you reach out to others for help.