First - bless you for rescuing these guys. I love to see abandoned animals find love and affection and a permanent home.
I would start with something simple to begin with. I would assume that these guys probably have fleas and the incessent scratching is what is leading to the hairloss and skin problems.
I would invest in 2 products - Capstar which will give them immediate relief from the biting within an hour and then also a proven/safe monthly topical treatment. I would suggest either Frontline, Advantage or Revolution (no revolution if the dogs are collies or collie mixes). Once you have treated with the Capstar orally, then treat with the other and they should be good for 30 days.
If neither of these help, then your vet is going to have to do a skin scraping to see if they have mange or some other parasite causing this. Below is a list of organizations that can help people who are having financial problems and are unable to vet their animals.
American Animal Hospital Association http://www.aahahelpingpets.org/ " Through the AAHA Helping Pets Fund, veterinary care is possible for sick or injured pets even if they have been abandoned or if their owner is experiencing financial hardship." Angels 4 Animals http://www.angels4animals.org/ "Our services range from financial aid to complete treatment to those pets and pet owners in need." Care Credit http://www.carecredit.com/ A credit card company for health care, including veterinary care. "With a comprehensive range of plan options, for treatment or procedure fees from $1 to over $25,000, we offer a plan and a low monthly payment to fit comfortably into almost every budget." God's Creatures Ministry http://www.all-creatures.org/gcm/help-cf.html "This fund helps pay for veterinarian bills for those who need help." Help-A-Pet http://www.help-a-pet.org/home.html "Our efforts focus on serving the elderly, the disabled, and the working poor." IMOM http://www.imom.org/ "We are dedicated to insure that no companion animal has to be euthanized simply because their caretaker is financially challenged." The Pet Fund http://thepetfund.com/ "The Pet Fund is a registered 501(c)3 nonprofit association that provides financial assistance to owners of domestic animals who need urgent veterinary care." United Animal Nations http://www.uan.org/lifeline/index.html "The mission of LifeLine is to help homeless or recently rescued animals suffering from life-threatening conditions that require specific and immediate emergency veterinary care. We strive to serve Good Samaritans and rescue groups who take in sick or injured animals. In certain cases, LifeLine can also assist senior citizens and low-income families pay for immediate emergency veterinary care." They also keep a list of local and national help resources here http://www.uan.org/index.cfm?navid=163
Good luck and let me know if I can help further!!!!
What flea treatment are you using?
Okay....Interceptor is a Heartworm/ hookworm product - it's not for fleas. I'll bet your problem is simply that. I would get some Capstar and Some Frontline or Advantix for dogs which also kills mosquitos and ticks.....You can order online, or purchase from a local pet supply in most cases.