What is the best way to advise a father and brothers who do not pray, knowing that the mosque is close to the home, and how can the second brother in the family do this?

You must supplicate for your father and brothers, asking for their guidance and the rectification of their hearts. You should also advise them and remind them of the seriousness of neglecting prayer, while utilizing available da'wah (proselytizing) methods and maintaining gentleness and kindness. If they respond, then praise be to Allah; otherwise, you will have fulfilled your duty.