Translation of "Else's" in Chinese

I entered someone else's room by mistake.

我不小心进错了别人的房间。

This isn't my umbrella; it's somebody else's.

這把傘不是我的，是別人的。

- Is this "giving sermons" or "sticking one's nose in someone else's business"?
- Is this patronizing or meddling in someone else's business?

「好為人師」還是「好管閒事」?