HolQeD 9:3 p. 8, matlh jup mu'mey:

vIn, in its plural form vInpu', is used for a group consisting of at least one tey' and no one who is not a loror a tey'. Thus vInpu' may be translated "cousins, nieces, nephews." If it's not a mixed group, then, of course, the plural forms of lor and tey' would be used (lorpu', tey'pu'). vInpu' might also be used if the speaker is unsure about the makeup of the group (but sure enough to know that vInpu'is a better choice than yurpu'. The singular form, vIn, is also sometimes used in place of lor or tey' when focusing on the vIn as a member of a group of vInpu' as opposed to his or her specific relationship to the speaker.

Learn more about this word at this HolQeD article.