Anyone know what disease this person could have?

Osteoporosis.

The low mineral and vitamin D levels are your key indicator there. Bones become strong through calcium absorption, which needs vitamin D for the body to be able to process calcium. Vitamin D is easily obtained through exposing the skin through sunlight, so going out on overcast days only will limit vitamin D synthesis. Milk is a good source of calcium, so not drinking milk or taking other dairy products can cause a calcium deficiency. Osteoporosis causes bones to fracture easily, such as breaking 2 ribs after a fall.

Fridays has it spot on!!! I suffer from severe vitamin d deficiency and have all of these symptoms on my list. Take grandpa to the doctors and ask for a blood test. Don't back down on this some doctors get cocky when you suggest something they didn't think of. Mine did and I suffered for 3 years before I got smart enough to get another doctor. My levels were at 13 and your suppose to be between 50 and 80. The old levels doctors recommended were between 20-50 but were found to be to low. I take a prescription of 50,000 IU of D2 once weekly now. I feel so much better. It seems strange that so much can come from a vitamin deficiency but all you need is to see the forums on vitamin d deficiency to see the same wreckage.

He's most likely suffering from Osteomalacia.

Here's more info about it: http://www.medicalook.com/Bone_diseases/Osteomalac...