Complex sentence: Their entry was selected through the national selection "Junior Songfestival 2017", which consisted of six contestants, divided into two semifinals, taking place on 2 September 2017 and 9 September 2017.
Split into simpler sentences: Their entry was selected through the national selection "Junior Songfestival 2017". It consisted of six contestants who were divided into two semifinals, taking place on 2 September 2017 and 9 September 2017.