Step parenting

So about a year ago I started dating a guy who already had a couple young kids. I just recently met them for the first time. I’m not entirely sure how to do the step mother thing, or even if I should. I feel my boyfriend doesn’t discipline them really at all. They cuss all the time and don’t clean up after themselves. Their mother lets them get away with whatever they want and he apparently doesn’t want to be the bad guy. When him and her broke up the kids decided to stay with him and refused to live with her, he adores his kids and is terrified of losing them to her. I tried to give him some advice but I don’t really feel it’s my place to do such. He didn’t take my advice about the kids really ever, which doesn’t really help me feeling like it’s not my place. I don’t have children of my own, and I cannot have them, so having a boyfriend that already had some was exciting, but now that I’ve met them and interacted with them I’m just feeling a little unsure.