Complex sentence: Before they were Big Fun, Creswick and John were in another regroup of Ian Levine's boy band Seventh Avenue with Mark Long and Steve Crawley who provide lead vocals for the group recording and singing live, performing in nightclubs all over the UK.
Split into simpler sentences: Before they were Big Fun, Creswick and John were in another regroup of Ian Levine's boy band Seventh Avenue with Mark Long. The other member of the group at that time was Steve Crawley who provided lead vocals for the group recording and singing live whilst performing in nightclubs all over the UK.