In need of advice. (family dynamics...)

First off I know everyone's family is different so I should rely on my best judgement in handling this sort of thing, but I really need some opinions on the matter.

I am out to my family, I have been for a year. We do not talk much about it, but we do not avoid the subject. However, my stepsister seems not to have told my nephews yet. They are 9 and 7.

How do I know that she hasn't? Well, the other day they were visiting and they got in an argument. This led to them calling each other gay. As an insult. Right in front of me AND their mom (my stepsister). She didn't say a word..

This is not the first time they have said this to each other either.

Now I don't know if I should be upset with her or not. Her and her boyfriend (the baby daddy) are not the most mature couple. So I am certain the boys picked it up from them saying it before I came out.

On top of that, I don't know if it is my place to tell my nephews that I am gay. Don't get me wrong, I don't mind sitting them down and explaining and answering their questions, but I feel like it is something their mom should do.

So, I am considering talking to my stepsister about it. I just don't know how to bring up the subject. And I don't really know what to say. The last thing I want is for her to feel like I am trying to tell her how to parent, but this is starting to feel like the closet again... And we all know how much fun that is /s.

I also don't know if I am making this a bigger deal than it actually is..