Does righteousness mean that one's parents are pleased, or that children do not fall short in their duties towards them? Is it permissible for a brother to act like his siblings who visit their parents only rarely, even though he fears harm befalling them?

Serving one's parents is an obligation upon their children, to be done with kindness. If you have brothers and a sister, then this service is incumbent upon all of you. You are permitted to ask your siblings to take turns with you in serving your parents. If they refuse, you are not allowed to abandon your parents without sufficient care.

Caring for and serving one's parents in their old age and sickness is a great deed, one of the best acts of proximity (to Allah) that Allah loves. It is one of the greatest causes of His pleasure and success, and it is a door to jihad. So be patient if they become angry with you, seek your reward (from Allah), and respond to that with kindness, humility, and reverence.

Their conduct towards you in this manner might be an indication of their excessive love and trust in you. So seek help from Allah and do not despair, and remember the greatness of the reward. If you fulfill your obligations of righteousness, care, and kindness towards them, then their dissatisfaction with you will not harm you.