Dear Mr Kishore Mullick,
It seems that your father in law is exhibiting signs of disease progression. Unfortunately, Parkinson's disease is incurable and despite medical treatment the disease progresses. Therefore he needs to be under regular follow-up with the specialist who will assess whether there needs to be a dose increase in his current medicines or any change to the medicines he is taking. Constipation
is a common and troubling side effect with Parkinson's disease. The disease itself causes the constipation and most of anti-parkinson's medicines aggravate it. Therefore, he needs to ensure adequate fibre intake in the diet, adequate fluid intake. Stool softners and laxatives will also help.
Hope this helps.