Ah India. That may explain the difference in treatment suggestions. In the uk he would probably have been given hormone tablets or injections to castrate him rather than surgical removal of the testicles but perhaps the hormones are hard to get in India. Surgical removal of the prostate is quite a difficult operation and can lead to impotence and incontinence - again, it may be difficult for a man of 76 to cope with incontinence in India, particularly if pads etc are very expensive.
You could seek a second opinion about gaving the prostate removed but best wait for the scans first - no point if it has already spread and if it hasn't spread you could maybe ask whether hormone treatment is available?