What is the ruling on employed children asking their sick father – who has income from rentals – to spend on them just as he spends on their unemployed siblings?

A father must financially support his poor children who are unable to earn a living, provided that something remains from his own expenses after covering his and his wife's needs. This is based on the saying of the Prophet, peace and blessings be upon him: "Begin with yourself, then with those whom you are responsible for supporting." He is not obligated to support wealthy sons and daughters.