Am I entitled to discuss with my father the money I send to them, and what is the correct procedure I should take so as not to fall into the sin of undutifulness towards parents, knowing that he spends the money on needy families and borrows for that, while he does not spend on my sister who is in difficult circumstances, and this spending affects my personal finances and my inability to save?

There is no harm in reviewing with the father the money sent to the family, and it is not obligatory to give him anything if he possesses what suffices him. The father must be treated with politeness, gentleness, humility, and reverence to avoid disobedience. Spending on one's wife and children takes precedence over others, and a balance should be struck between generously providing for relatives and saving if surplus money is available.