Is it permissible to take what remains of the pension of my father, who lives with me and is fully served and cared for, even though he lacks nothing, and my siblings rarely visit him?

It is not permissible to take anything from the father's money except with his permission and his goodwill, due to the Prophet's (peace and blessings be upon him) saying: "The wealth of a Muslim man is not lawful to his brother except what he gives him willingly." Serving one's father is an act of righteousness commanded by Islamic law, and it is an honor and a reward that a child can never fully repay. One should seek the reward from Allah without boasting about it.