If you need to be more specific, it can stated what they were amazed by. AT: "They were completely amazed at what he had done" (See: [[rc://en/ta/man/translate/figs-explicit]])
Here the phrase "the loaves" refers to when Jesus multiplied the loaves of bread. AT: "what it meant when Jesus multiplied the loaves of bread" or "what it meant when Jesus caused the few loaves to become many" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Having a hard heart represents being too stubborn to understand. AT: "they were too stubborn to understand" (See: [[rc://en/ta/man/translate/figs-metaphor]])