How to get the toddler to use the potty by himself?

We're trying to potty train my little brother, and he was doing well at first when we would usher him to the potty and stay in there with him and then he'd get a treat afterwards. But now that we stopped going in with him, he'll still come tell us that he has to go potty, but he'll usually pee on the floor outside of the potty and soak his underwear and then come running back to us naked saying his underwear is dirty. My older sister started putting him back in pull-ups, but my mom doesn't want to go back to those.

Is there any way to get him to use the bathroom by himself? He'll usually do it once a day, but then the other times not make it.