Complex sentence: The three founding members Argyris Tsoukalas, Ilias Goulas and Adamantine Arvanitis had met in 1999, in a local school's graduation concert and played together for a while,' till Argyris Tsoukalas left for Italy for study-related reasons.
Split into simpler sentences: The three founding members (Argyris Tsoukalas, Ilias Goulas and Adamantine Arvanitis) had met in 1999 in a local school's graduation concert. They played together for a while, until Argyris Tsoukalas left for Italy for study-related reasons.