I don't know what is goin on with my youngest son but I'm not liking these changes he's made these…

I don't know what is goin on with my youngest son but I'm not liking these changes he's made these last few months. He treats his 4yo step sister so bad and also keeps having this really bad attitude towards everyone. not to mention the lies and stealing too. I hope I can somewhat get him straightened out before this baby is born cause I can't deal with all this. I'm beginning to wonder if he feels like he's being replaced cause he's been the youngest for so long and we've only recently been able to get our 4yo on a regular basis. Not to mention now we r having a baby and his father who only sees him 1 day a week is also having yet another kid. Any advice to deal with this would b helpful. I'm gonna try to get him in counseling so maybe he will talk to someone but idk how that is gonna go cause he's always so quiet