Foot swelling and pain in the elderly

Not sure where else to ask this...
My dads(64years young) foot has been swollen off and on, for almost 9 months. It gets close to double in size. He's on crutches and a foot brace while occasionally using the sauna, and primarily watching TV in bed. His foot swelling will go down but any sort of pressure makes it flare right back up(he cannot drive because of pain). His doctor misdiagnosed him twice. Now he's saying it's a stress fracture.

I'm curious if anyone has had experience with something along these lines? He will feel better for a day and not need crutches then do something dumb like chop firewood or start gardening, for it to come back just as bad. We're all worried. Diabetes also runs in the family, my grandfather had to get his foot amputated before he passed because of it.

He hates going to the doctor and his primary has misdiagnosed him in the past. I've tried to get him to see mine but he refuses.

Does it sound like a normal stress fracture?
Could it be related to something completely different?
Can an untreated stress fracture be deadly for the elderly?

In starting to think he won't be walking again and it kills me. Any input is greatly appreciated.