At first sister-in-law returns and resides among Irish people, perhaps, and musicians (8)
I believe the answer is:
cellists
'musicians' is the definition.
(cellist is a kind of musician)
'at first sister-in-law returns and resides among irish people perhaps' is the wordplay.
I cannot really see how this works, but
'first' could be 'ist' (ist resembles 1st) and 'ist' is present in the answer.
The remaining letters 'cells' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'and' is the link.
Can you help me to learn more?
(Other definitions for cellists that I've seen before include "String players" , "Julian Lloyd Weber and Jacqueline du Pre, say" .)