It sounds like your father is experiencing a case of dermatitis or eczema (inflammation of the skin).
Dry skin due to increased age and swelling due to poorly functioning leg veins, are predisposing factors for this condition.
Gravitational dermatitis or eczema is a itchy rash that appears at the swollen lower legs of elderly.
The legs are red, scaly and itchy.
Swelling is also a feature of eczema.
Further, it can be complicated by nummular or discoid eczema (pink, red, brown well-defined patches with a dry cracked surface or bumpy, blistered or crusted surface).
Discoid eczema can be extremely itchy and the rash may persist for weeks or months.
There is chance for bacterial secondary infection of eczema rash.

Consult dermatologist for eczema and vascular surgeon for possible vein problems.

Best wishes!
Marija