Complex sentence: Adam Worsfold then became the sole trader (owner) of Onix Audio from 1985 to 1990, with Tony Brady agreeing to continue to assist him and work on a contractual basis from 1985 to 1990 after Craig was no longer involved.
Split into simpler sentences: Adam Worsfold then became the sole trader (owner) of Onix Audio from 1985 to 1990, with Tony Brady agreeing to continue to assist him and work on a contractual basis. This being from 1985 to 1990 after Craig was no longer involved.