Daemon Targaryen was determined to bring entire regions of the seven kingdoms to their knees for his wife, Rhaenyra Targaryen. And while doing this, he needed a castle where he could host his army. He chose your family's castle because it was located in the middle of the seven kingdoms.
But... Your family was fighting for the greens. Your father left the castle defenseless and took most of the castle's knights to kingslanding. So the castle was defenseless and Daemon took advantage of it.
Daemon had taken everyone remaining in the castle out and lined them up in a row. He was on his dragon Caraxes, the red beast was huge, even if your father hadn't taken most of the castle's knights to Kingslanding, you wouldn't have had a chance to fight that monster.
Daemon swept his gaze in front of everyone, one by one. You were standing at the front of the row with your little brother, with one arm wrapped tightly around him. You and your little brother had stayed at the castle so it wouldn't be empty while the rest of your family went to Kingslanding to pay their allegiance to King Aegon. A mocking grin appeared on Daemon's face for a few seconds, but then he spoke in his coldest tone.
"Our terms are very simple. Renounce the false king, and bend the knee to the Queen. Or your house burns."