Welcome to HCM,
After going through your father,s history he has two medical issues first is Rheumatoid arthritis
and Cardiomyopathy ,please understand he must be having these both for quite some time but as he became symptomatic for cellulitis they are diagnosed hence take good care of him.
Cardiomyopathy with LVF (Low Ejection Fraction) that is why salt and fluid is restricted and cardiac drugs are prescribed with diuretics and ACE inhibitors.
His declining immunity may be result of use of Oncotrex as it is a immunosuppressive drug
, partly and by disease itself.
You can visit good hospital and consult a Cardiologist
to help him, once he is investigated and if required re-synchronization with ICD may be advised and would benefit and his pain and inflammation can be controlled with drugs.judiciously.
For heart of end stage Heart transplantation
if possible is also possible.