Certain drugs can end up causing gastritis. You mentioned your father was on 8-9 pills for various reasons. It'll be better you could mention their names. Or better still, take him to your physician. Secondly, avoid spicy and only food at bed time. Maintain a 2 hr gap after dinner and then sleep. If he has reflux issues. He should avoid sleeping flat and take antacids

Hello there....., your father should follow a combination of healthy diet and exercise – aim to reduce dietary intake of fat, salt, and sugar, increase intake of fruit and vegetables, and consume mainly low glycaemic index foods. A minimum of two hours of moderate intensity exercise should be undertaken each week., along with the prescribed medications....