This is a case of acute gastric reflux, common at old age due to sedentary lifestyle. I would suggest a gastric endoscopy to rule out any ulceration. Are there any symptoms of nausea, vomiting, or blood stained vomit? Do your parents immediately take rest post meal? Kindly connect for further management discussion
Next Steps
Minimal physical activity post meal
avoid drinking water immediately post meal
proper timing of food consumption
avoid spicy oily fat food