Nervous and stressed 😣 ADVICE PLEASE! !

My SO already has 2 kids, they are 8 and 5 and they don't listen at all due to them spending more time at their mom's house. I am currently almost 30 weeks pregnant and dreading the day the baby comes because of my step kids. I honestly cannot handle them anymore even now, they lie every chance they get, they steal and leave all the lights on in the house (which increases out power bill) they just don't listen at all. I've known them for over 3 years now and it's only getting worse. Please no hate I just can't physically handle them anymore and my SO is also at his last rope with them. I am at a complete loss and stressing out. I feel like pulling out my hair, and honestly am not looking forward to all of this when the baby comes. We have tried everything to correct their behavior and yet nothing has changed. Please, please any advice would be GREATLY appreciated!