To further clarify my previous post, here are some Chinese sibling address/honorifics ranked loosely from normal to cursed, using sy as an example:
(Please note that family honorifics can be very regional. I'm sure there are more that aren't on this list)
For a younger sibling, when referring to an older brother:
San-ge - Yes. literally means "third brother". Da-ge for firstborn, er-ge for second etc. Sometimes sons and daughters are ranked separately. So a son who's the fifth child of the family but the third son might still be San-ge.
Gege - Only if you're young, or have a large age gap, or just being cutesy uwu. Might sound a bit weird coming from a grown man, a bit more acceptable for women.
Shen Yuan (full name) - Really depends on your relationship. I know some twins who do this, but also some who don't. In chinese culture twins are still considered older/younger, depending on which one of you came out first.
Yuan-ge - No, unless you're trying to be funny.
A-Yuan, Yuan-er etc. - Doubly no.
For an older sibling, when referring to a younger brother:
A-Yuan - Regional, so sometimes yes.
Xiao-di - This is usually reserved for the youngest brother in the family.
Didi - Sure, but very cutesy sounding.
Yuan - No (see explanation below).
In Chinese, you never address someone with a single-syllable given name by their given name alone. This is partially due to the fact that there are often over a hundred characters with the same pronunciation, and saying a single syllable can lead to confusion. Are you saying someone's name or mean something else entirely? It's almost impossible to tell.
However, when someone has a two character name like Shen Qing-qiu, then yes, an older sibling can call him Qingqiu.