My dad has killer knee pain, is there anything my mom and I can do to help?

It is likely that his kneecap is popping in and out of place. EXACT same thing only happened to me, except after the first time I was in unbearable pain. So I went to ER. They diagnosed it as a sprain and had me follow up with an orthopedic doctor a week later. He said ACL sprain and ordered an MRI to confirm it. The MRI confirmed that I had torn cartilage and not my ACL, it also showed bone bruising consistent with a dislocated kneecap. So I'd say have him stay off of it as much as possible and have him keep it straight. Really no point in buying an immobilizer if he's seeing the doc on Monday. If you already have one at your house, have him put it on. Elevate if ever possible to take swelling down. Not really much else you can do to help him. He can take up to four Tylenol or Advil instead of two. Four is equal to a prescription dose. Don't worry if it is kneecap issues it's not anything to be scared of. Very easily fixed with PT