<human>: Can you give me the gist of the text in a nutshell?

I have a step brother (age 16) in High school whom every day, comes home with his girlfriend, spends all day with her, and then she goes home. Or some form of spending all the time together.

He barely is seen around the house, hardly helps out around the place.

My sister is nearly the same, but its in an unhealthy way. 

I feel what they are getting into isn't healthy and my parents set very bad relationship skills on the kids. They got a divorce and after two years it finally was "finalize" just recently.

Ive only seen my sister and her bf fight before, never my step brother and his SO but I feel they spend too much time with them over all and its not going to be healthy. Step brother doesn't really have any true hobbies, skill sets, and I worry about my brother more then my sister in the end. I don't know how to reach out to him.

Sister is 20, but entering that stage where she could end up marrying this guy. And shes beginning to realize that the guy is manipulative and the best guy when it comes down to it.
<bot>: Is it healthy for a sibling to spend all their free time with their girlfriend/boyfriend, and hardly be around the house, and when they are they do the bare minimum of contributing.