Welcome! If your dad has acid reflux, then Nexium or similar would help. My wife has taken it when she has been on chemo and it caused that temporarily.
As for eating, it is probably best to try small snacks every two or three hours rather than three big meals. It also lessens the nausea. You can use easy to swallow things like Ensure, Breeze, Smoothies, Frosties, blender stuff. Good that you guys are taking turns helping the parents out. Don