I'm not sure why she needs to tell them she is gay or to make a huge deal out it. Are they planning on making out or something in front of them to where they would even question anything other than friendship?

There are appropriate behaviors around kids and family, no matter what their sexual orientations are. I understand of wanting to be oneself, but when you are visiting and staying in the home of your parents (are they staying with you?), you must respect and take in consideration of what is appropriate behaviors in front of their children and their own parents.. I don't know of any parent who would want to see or hear sexual escapades of their adult children in their home (even married adult children)

I have a 20 year old daughter and I wouldn't allow her to stay in my home with a partner/boyfriend/girlfriend (in the same bedroom) if I had young children at home. It wouldn't be the values I would want modeled for very impressionable young kids, especially from an older sibling. It would be different if they were married. As far as being gay, most kids already know about this, it isn't anything shocking or new to them.