What do you call your father's twin brother? I'm a mid-level Chinese student.  I have two younger brothers, who are twins.  One brother is married to a Chinese woman, and they have a young son.

The son calls me 姑姑 and my husband 姑丈.  My sister-in-law's younger brother, his maternal uncle, is 舅舅.  So far, so good!  My question is, what should he call my other brother, his paternal uncle?

The trick is that we don't know which twin is older.  Our parents refused to tell us growing up to avoid fostering (more) power plays, and now claim to have forgotten.  We can't be the first family in history to have siblings that aren't fully ordered, but we can't figure out if there's an accepted word for a twin uncle in this scenario, or we should just pick whichever of 伯伯 or 叔叔 we like better.
How about 伯叔? That is an actual thing when you don't want to specify the age.

See here:
https://www.moedict.tw/%E4%BC%AF%E5%8F%94