Complex sentence: Since 1998, the band's constant members have been lead vocalist Joel Madden, lead guitarist and vocalist Benji Madden, bassist Paul Thomas, rhythm guitarist and keyboardist Billy Martin and drummer is Dean Butterworth, who has been a member of the band since 2005.
Split into simpler sentences: Since 1998, the band's constant members have been lead vocalist Joel Madden, guitarist and vocalist Benji Madden, bassist Paul Thomas, and guitarist and keyboardist Billy Martin. Their drummer is Dean Butterworth, who has been a member of the band since 2005.