What should a son do who has spent a lot on his father and siblings, and when he apologized for a sum requested by his father (because he wants his father to rely on himself, and he is financially exhausted), is this disobedience to parents?

Filial piety is one of the greatest acts of devotion. It is achieved through good treatment, care, and financial support when needed. If the father is not in actual need of money, you are not obliged to give it to him. You can use an indirect phrase that preserves affection, such as saying, "I don't have [it]," meaning, "I don't have [it] now." The hadith (definition) "You and your wealth belong to your father" is not to be taken literally, for the father may take from his son's wealth only to the extent of his need and provided that certain conditions and regulations are met.