I have to agree with nomad1, those are the best avenues to follow. I don't think letters written to individuals would go over very well. It's unfortunate but that's how it often turns out. Do you belong to a church? I think it would be appropriate to let your pastor in on what's going on and ask him or her if they could start a drive for help for your family. I only know things that might work here in the U.S., but if you are here you might even contact someone from a local TV station. I would think the place to start there might be the reporter who handles the "On Your Side" or "In Your Corner" features. That person should be able to put you in touch with someone, or perhaps even help you himself. Good luck, and I will sure keep your family in my prayers.
I don't know if your in the U.S. Or not but if you are you could contact the shriners,churches,children's hospital, there are tons of charitable organizations that will help and maybe even cover the whole bill for the surgery. Just explain your need as best you can and send letters to everyone you can. The ronald mc donald house comes to mind in the case of housing during the surgery. www.rmhc.com