All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
First of all, may Allaah reward you for being keen on gaining lawful earnings; we ask Allaah to make you firm and steadfast on the truth, guide you to do good, open your breast, facilitate your matters and bless you with lawful and blessed provision.
You should know first that there is a difference between the wealth of the father being entirely ill-gotten wealth and his wealth being mixed with lawful and forbidden earnings. It is forbidden to eat from his wealth if it is entirely ill-gotten wealth, but it is only disliked and not forbidden if his wealth is mixed between lawful and ill-gotten. For more on ill-gotten wealth, please refer to Fataawa 87680 and 91257.
Even if we presume that the entire wealth of your father is ill-gotten, you are not sinful for what he spent on you while you were young. However, what he spent on you once you became pubescent - and you know that his earnings are ill-gotten - it is a sin to have eaten from it unless you were in a state of necessity to do so. However, you are not obliged to guarantee this wealth for its owners, because the wealth from gambling is taken from its owner with his consent. Since this is the case, you are not obliged to give it back to him.
Shaykh Ibn ‘Uthaymeen said in the Fataawa of "Noorun ‘ala Ad-Darb": "If one had taken the money with a contract, transaction or exchange (in which compensation is given against the goods or services received) from its owners, then he is not obliged to give it back to them, just like the gambling money which the questioner mentioned that he used to take, as this is due to a contract in which there is agreement with the other party, so he is not obliged to give back to him what he had taken from him. He should instead give it in charity as a way of getting rid of it [ill-gotten wealth] and he should not give it back to its owner because if he gives it back to its owner, he would make him take the the thing and its compensation at the same time....."
On the other hand, you should advise your father and clarify to him that he is obliged to sincerely repent. Among the steps of fulfilling sincere repentance from what he did is that he should get rid of whatever ill-gotten wealth that he has at hand by spending it in charitable fields. You should advise him in a soft and gentle manner so that he might be deterred or fear Allaah.
Finally, we advise you to look for suitable and lawful earnings and not despair because it is the devil who makes us do so. Moreover, you should be keen on mixing with and keeping company with righteous people and supplicate to Allaah as much as possible.
Allaah Knows best.