One selfie features the trio snuggled up in the grass together, while the remaining shots showcase Bo hanging out by guitars, in the grass, and on the couch.
"Baby boy Bo. Stay safe everyone," Simpson captioned the post, referencing the ongoing coronavirus pandemic.
Cyrus, 27, announced that she adopted Bo on her Instagram Live show, Bright Minded, earlier this week.
At the time, Cyrus revealed that she adopted the pup from The Wagmor Luxury Spa, Hotel & Rescue in Studio City, California, and named him after her dad, Billy Ray Cyrus. According to the singer, her famous father went by the nickname Bo in high school.
Watch the video below for more on Bright Minded.