A person will not pray consistently unless they understand why they have to do it. They will either pray because someone just told them to, or to show off, every reason except for the sake of Allah. I remember being told to pray by my parents and I would go in the room, sit down for 5 minutes and come back to act like I prayed. Why? Because of the lack of understanding of why it had to be done.
How did the situation change? When my environment changed slightly. I went to Islamic conferences and Itikaaf
just because my friends were going and Alhamdulilah, being in that environment, being forced to listen to the talks about deen somehow affected my heart and gave me enough reason to return home and begin praying for Allah. It didn't stop there and I had to keep the momentum going or else I would lose it and that was done by continually exposing myself to that environment and slowly but surely the haram actions began to fade.
So that is one method of trying to bring about change. Maybe ask him to take you to an Islamic conference and say that he should remain with you until it is over. Don't tell him that he should listen to it, but just be there. Start with small ones because he might not have the patience to stick around at the longer ones unless he was just 'chilling' with friends.
I don't know your brother or your situation, but the idea is to get him somewhere where he will involuntarily listen to talks about deen.
May Allah bring us on as Siraat al Mustaqeem.
