What is the ruling on the fasting of one who fasts but does not pray, and what can be done regarding them?

You must advise your father and brother to repent from abandoning prayer, and warn them of Allah Almighty's punishment. Allah has promised perdition (Ghayy) for those who neglect prayer, and Ghayy is a valley in Hell, as Allah Almighty says: "Then, there succeeded them a generation who neglected prayers and followed their lusts. So they will be thrown in Ghayy. Except those who repent." Among the things that will help convince them is to bring audiotapes and booklets that discuss the importance of prayer and the danger of abandoning it.