What is meant by redressing grievances and restoring rights to their owners? Is the Hajj considered valid if the father pays for its expenses? Is it a condition of Hajj for the pilgrim to pay all of their own expenses?

Returning injustices and rights to their rightful owners is an obligation upon a Muslim, whether they are material possessions or intangible rights. If these rights cannot be restored, such as backbiting, then forgiveness must be sought from those who were wronged without explicitly stating the act of backbiting. Repentance to Allah is obligatory at all times, especially before Hajj or Umrah (definition). It is the return from disobedience to obedience, and it is a cause for success and Allah's love. There is no harm if a father or anyone else pays for the expenses of Hajj; the Hajj is valid for the pilgrim, and whoever spent on it will be rewarded. As for books related to Hajj, there are many, and one can refer to the library sections, fatwas, or audio materials on the website.