Relative ease at first in part of Ulster church (5)
I believe the answer is:
niece
'relative' is the definition.
(type of relative)
'ease at first in part of ulster church' is the wordplay.
'at first' indicates taking the first letters.
'part of' indicates anagramming the letters (I've seen 'parts of' mean this).
'ulster church' becomes 'ce' (I can't explain this - if you can you should give a lot more credence to this answer).
The initial letter of 'ease' is 'e'.
'e'+'in'='ein'
'ein' anagrammed gives 'nie'.
'nie'+'ce'='NIECE'
Can you help me to learn more?
(Other definitions for niece that I've seen before include "Family relation" , "Brother's daughter" , "Family girl" , "Brother or sister's daughter" , "Daughter of a sibling" .)