The phrase "to become family pets" means that animals have been adopted into a human family and are now living with them as companions. Full definition
They became more than a weekend chore or just little egg - laying machines and have really become family pets. (techsavvymama.com)
With her brothers off to college, subsequent «hunting dogs» soon became family pets. (karenpryoracademy.com)
«In August 2015, mild - mannered mutt Bagel became a family pet for ProSocial's CEO, Meredith, and her husband and their two boys, soon after an animal rescue organization in Los Angeles, Wags & Walks, found the dog living on the streets and determined she'd been deliberately abandoned by her owners. (wagsandwalks.org)