C.P.
Just tell him no and never give in.
Ever.
When he gets out of bed, take him back. No talking, no arguing, nothing. Every time. Back into the bed and walk out. He sleeps in his own bed, no nightlights in his room, no music, nothing. He doesn't need it. What he needs is consistency.
The key is that you STOP arguing with him. A firm, but quiet "no." And then you take him by the hand and take him back to bed. You MUST get up from what you are doing and physically put him back into bed. This might require you silently sitting outside his door for an hour the first few nights. Just keep doing it until he realizes that there is no getting past you and no wearing you down. Get dad in on it too.
Remember, no yelling or arguing. Just "No. Back in bed." Put him there and walk out. Every time.
I know it's hard, but push through it. The rewards are worth it!