How would you handle this situation?

Five months ago, my brother posted that he needed someone to watch his 7 year old dog for a while until he found a new place to live. I'm not close with him, but decided to reach out for the dog's sake. He said it would be 3 months tops and would send the money for anything she needed. My husband and I lived out of state at the time so we asked my husband's sister and fiancé since they own a house and have 3 acres of land. Even though they have two labs, they agreed to watch her. After a month, they decided enough was enough since my brother wasn't returning phone calls and texts. My husband's parents then took his dog in. My husband and I and his parents have put so much money into her by switching her food to something more nutritious, getting her checked up at the vet, getting her groomed, and getting her on monthly heartworm. I won't complain though since she seems happier and is getting healthier (was very overweight and needed to be groomed since she has a long fur coat and had lots of knots). Meanwhile, my brother hasn't sent a single check and hasn't once asked how she was doing. Definitely had no intentions of ever picking her up ever again. He then goes and gets another dog! I am so livid I could cry and don't know how to handle this situation or how to tell my in laws. I am honestly so embarrassed that I'm even related to the guy considering how neglectful he is.