dog co ownership and ownership

I have a dog that I picked up from the previous owner who purchased the dog. The breeder and owner agreed for her to come stay here. She has been with me for 5 months now and is very happy and content. The previous owner has a signed co ownership and contract to which neither one has been cancelled. The breeder then sent me a signed co ownership but i have no contract with the breeder for this dog. The breeder did not want this dog in the beginning and now wants to take her from me. Do I have any rights?, can the breeder take the dog? If persued can I charge the breeder board and any medical expenses that has occured. Who legally owns this dog? I don't care about the paperwork my main concern is the well being of this dog. She has become part of my family and i do not want to give her up.

Unless they gave or sold the dog to you, they unfortunately normally retain the right to take it back. And you really cannot charge them unless that was agreed.