Complex sentence: The New Zealand U19 Schoolboys will also play exhibition matches against professional clubs, Sydney FC and Western Sydney Wanderers, who are amongst the strongest clubs in Australia's highest professional league, the Hyundai A-League.
Split into simpler sentences: The New Zealand U19 Schoolboys will also play exhibition matches against professional clubs, Sydney FC and Western Sydney Wanderers. They're both among the strongest clubs in Australia's highest professional league, the Hyundai A-League.