I would say that he does care and knows the old man is his dad.
But he is also scared that if he disobeys the demon lord he would lose everything and he doesn't believe that the demon lord would lose this conflict.
He knows its wrong, but he doesn't want to fight.
At this point, you can´t really blame his as he is effectively being indirectly forced to do everything under duress of his life.
Sadly this type of stories usually doesn't end well for characters like him even if they aren't necessarily evil.
They tend to be sacrificed by the big bad evil guys to get one last power boost and stuff like that.