a questions for americans about language?

no way

unless they are homo or something

Those are simply terms of affection thrown around by many people in an informal setting. You won't see it in any official documents or formal letter writing unless she were in fact a Nun. Don't feel bad about not getting it. Some of us been here over 50 years still get confused with some of the new stuff. It involves knowledge of history, current events, newly released music lyrics, and an assortment of other considerations. Hope that helps

I call my two best friends my family. My brother, and my sister. We have often been confused for true family. Cousins and siblings - we get it all the time. It depends on the strength of the relationship. The bond that has developed between them. Friends are, after all, the family that we choose for ourselves.

I've never heard or seen anyone use "your sissy". That's for sure. Maybe sis and bro though. It's hard to generalize.

If they are from the South they may. My husband always refers to his Sister as "sis".

Maybe if the two have been friends for a long time and it's kind of a joke between the two of them...

Why are you asking? What business is someone else' email to you?

because they feel like they are close enough to be, "Family".

Ya, they can, if they're real creepy.

there's freedom in there you can do whatever you want