I certainly feel for you, and admire your dedication and sacrifice. I have had as many as 6 house dogs at once, and we could never afford all the veterinary care that some people can. So over the years I have taken it upon myself to learn as much, and do as much, as I could holistically with myself, my family, and my animals, and we have all benefited from it. That said, I will not offer you any advice, but suggest you search this: 'Home Remedies to Make Kidney Stones Dissolve'.
I don't think we are allowed to post links here, but if you search that, it should take you to a good piece on kidney stones, on a site called 'Live Strong'. It may give you some ideas that you may be able to use yourself and give you a little more feeling of control. This info may not eliminate the problem, but may help ease the discomfort.
I am a firm, lifelong believer in homeopathy. Not so much for any 'cures', but just that I believe it helps make and keep the body strong so that it can better fight it's own battles, and better it's odds of 'winning' those battles.
Keep us posted, and again, I admire your love for those in your charge.