Is it permissible to take from the donations that come to the father, which he spends on those undeserving, in order to give them to the deserving, such as widows and orphans, and without his knowledge?

The descriptions mentioned do not negate need in all cases. One who is capable of working might not find employment. Displaying oneself (tabarruj) and studying at a private university do not prevent one from being eligible for charity (sadaqah) and zakat if the person is in need. What is considered extravagance in marriage might not be so in every instance.

You should advise your father to give priority to those who are most deserving of charity, according to the donors' conditions. If he insists otherwise, you should alert the donors and the wealthy individuals.

Taking money without your father's knowledge is impermissible due to the potential for corruption and the intrusion of personal desires into charity funds for personal gain. You might accuse your father and take the money, and you might not be trustworthy with these funds.

In Sahih Muslim, the Messenger of Allah (peace be upon him) said to Abu Dharr: "O Abu Dharr, I see you as weak, and I love for you what I love for myself. Never be in charge of two people, and never handle the wealth of an orphan." Al-Nawawi said: "This hadith is a great principle for avoiding positions of authority."

Those whom you have described might be deserving according to the donors' conditions, and what you take might be from the share of the poor families to whom your father gives.