The shooting happened in the 4100-block of West Grenshaw Street at around 11 a.m.
Keith Glover said his 71-year-old father, James Sloan, and his 37-year-old brother, Tyrice Glover, were returning home from grocery shopping when a car pulled up and gunfire erupted.
Sloan, a retired CTA worker, was shot in the back and transported to Mt. Sinai Hospital in stable condition. Glover was transported to John H. Stroger Hospital in critical condition, police said.
"My dad is talking and alert, my brother right now he's in surgery, so we are just praying," said Glover.
Investigators at the scene said a motive for the shooting is unclear. Detectives canvassed the neighborhood to see if any security cameras captured the attack.
No one was in custody Thursday. Police are investigating.