드시다 is the respectful word for eating, and every line here is the same warm phrase 맛있는 거 드시다, hoping someone has something good to eat: 맛있는 거 드시면서 봐주시면 감사하겠습니다, 제일 맛있는 거 드셨으면 좋겠기에...!!, 밥은 맛있는 거 드셨을까요?. It works as a small kindness rather than a statement about food. Use 먹다 about yourself and 드시다 about the person you are speaking to or about respectfully.