Son now lives rent free in a house owned by family members. As I understand SSI, he is responsible for paying fair market for rent.I do not exactly see why your marginally healthy and at best marginally employed son should work so diligently to "keep his retirement" and do not understand why filing for Medicaid would cause him to "become homeless." In these challenging times, it may be harder for him to find further employment and SSI with Medicaid (assuming he has not worked enough and would not qualify for SSDI) sounds like an on-going solution to his need for medical treatments. I do believe I'd be willing to try to give up his particular doctors. I am sure there are some medical facilities in your area somewhere that accept Medicaid.
My first contact with SSDI applicant attorneys was not fruitful. They apparently did not think bipolar with multiple hospitalizations, O2 dependent sleep disorder on top of cancer and newly diagnosed rheumatoid arthritis and lung disease was worth their time.