When do sibling relationships become inappropriate?

Ja

I have a twin brother. He’s my best friend. We’re very close and everyone around us knows that. Lately, our friend group has started hanging out with more people and they’ve commented on us being so close and even said it’s “creepy.” They’re insinuating that we are inappropriate with one another and our actions are incestuous. I’m quite offended by this. I obviously don’t see my brother in a sexual or romantic light. I don’t know why our relationship has to be sexualized like that. So I’m asking what is and isn’t appropriate for siblings. To give you an idea of behaviors that are apparently inappropriate, they have noted me resting my head on his shoulder when I’m tired, the two of us sharing a blanket when sitting on the couch and watching a movie, and we slept in the same bed when on vacation. For contextual purposes, we are sixteen and both in romantic relationships. Our significant others don’t find our behaviors to be strange at all. We’re just twins who get along and are best friends. I am asking for outside opinions on not only mine and my brother’s relationship, but in general as well.