Complex sentence: He is also the founding lead vocalist and rhythm guitarist of the alternative rock band Jebediah, which was formed in 1994 and features his older brother Brett Mitchell, who joined on drums before the group's first performance.
Split into simpler sentences: He is also the founding lead vocalist and rhythm guitarist of the alternative rock band Jebediah which was formed in 1994. His older brother Brett Mitchell joined on drums before the group's first performance.