Everyone at home welcoming a church marriage (8)
I believe the answer is:
alliance
'marriage' is the definition.
(thesaurus)
'everyone at home welcoming a church' is the wordplay.
'everyone' becomes 'all' (I've seen this before).
'at home' becomes 'in' ('in' can be similar in meaning to 'at home').
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'church' becomes 'ce' (abbreviation for Church of England).
'in' enclosing 'a' is 'ian'.
'all'+'ian'+'ce'='ALLIANCE'
(Other definitions for alliance that I've seen before include "Federation" , "Coalition or union" , "Bond" , "Combination by treaty" , "match?" .)