This is such a sad and tough situation. I wouldn't be able to put down a healthy animal either. Since the family members are dog people and already have dogs and these cats have never been around dogs, I would try to find them another home together if at all possible. I know it's kitten season right now but maybe a rescue group could help these people find them homes. Many people also list their animals on Craigslist but you never know who you're going to get there and you should always charge a fee. They both sound like gorgeous cats. I wish them luck.