The responsibility of the eldest son of a family is to first take care of his own family, which is his wife and children. After that, he should take care of his parents if his parents are too old and needy, because the rights of parents are foremost and takes precedence over other people’s rights.
It is obligatory for the child to spend on his/her parents, if the parents are poor and he/she is rich. It is indicated in the Qur’an about the obligation of spending on the parents:
“And your Lord has decreed that you worship none but Him. And that you be dutiful to your parents.”(17:23)
Being dutiful to your parents include spending on them when they are needy.
As narrated from ‘Aisha that the Noble Prophet (peace and blessings be upon him) said; “Among the best of that which a man consumes is what he earns (by his own effort), and his son is part of that which he earns.”
Ibn al Mundhir said that: “The scholars are unanimously agreed that spending on poor parents who have no income or wealth is an obligation to the wealth of the child.”
A man once asked the Noble Prophet (peace and blessings be upon him); “Which of the people is most deserving of my good companionship?” The Prophet (Sallallahu ‘Alayhi wa Salam) replied; “Your mother.” He asked again; “Then who?” the Prophet (Sallallahu ‘Alayhi wa Salam) replied again; “Then your mother.” He asked again for the third time; “Then who?” He replied again; “Then Your mother.” He then asked again for the fourth time; “Then who?” The prophet (peace be upon him) said; “Then your father.”
It is also obligatory to spend on paternal and maternal grandfathers and grandmothers. This is the view of many of Islamic scholars, because the grandfather is also called a “father”. Allah (Subhanahu wa Ta’alla) says; “It is the religion of your father Ibrahim.”
And Allah (Subhanahu wa Ta’alla) says; “And marry not women whom your fathers married”. “Fathers” here means the father and the grandfather on both the mother’s and father’s side.
Allah (Subhanahu wa Ta’alla) then says; “For parents, a sixth share of inheritance to each if the deceased left children”. “Parents” here means both grandmother and grandfather. Grandmother is also referred to as mother.
Allah (Subhanahu wa Ta’alla) says: “Forbidden to you for marriage are; your mothers.” This includes mothers and grandmothers.
It is obligatory for the son to be dutiful and to spend on grandfathers and grandmothers too, for a grandfather is called a “father” and grandmother a “mother.”