This is not an easy situation as all the family needs to change, starting from your father to you personally.
Your father has to understand that neglecting his son and looking the other way would only make his situation worse. He has to discipline his son before it is too late. There will come a time and your father would not be around. It his son the man he hopes to take care of his family and continue his legacy?
Your brother is spoiled and he is enjoying being irresponsible and a bum. It is the family who helped him become that.
You have been pampering him for too long. He has to be rewarded when he does something good but he also has to be reprimanded when he does something bad. This is not being implemented.
For example, if he is late, there should be a curfew. If he doesn’t sit on the table with the family for meals, there is no food for him. If he complains that he is not a child any more, he is requested to prove it and to show us that he is a man by his actions.
He has to be forced to pray in the masjid or his allowance would be stopped. If he continue his behavior, the game must be stopped at any cost and he would not play it until he shows some improvements.
As for you, it seems that you are driven by the grace of Allah to advising them and giving them Dawah which is positive and good. However, your younger brother is looking for love and respect more than do’s and don’t’s. You should ease it a bit on the orders and give him more room. I am not saying the you allow him to sin but you should make him realize that by himself and through dialogue.
You have to sit down with your elder brother and have a similar dialogue. You should ask him about his objective in life and where is he planning to go from here.
May be if he is able to put his thoughts on the table, he would be able to see what kind of a person he is.