Joshua's father and sister (3)
I believe the answer is:
nun
I believe this clue is a double definition.
'joshua's father' is the first definition.
(Nun is the father of Joshua in the Bible)
'sister' is the second definition.
(sister is a term of address for a nun)
'and' is the link.
(Other definitions for nun that I've seen before include "Woman in Holy Orders" , "eg Carmelite" , "Member of convent" , "Black and white pigeon" , "Priory female" .)