In a statement Thursday, they asked for "consideration and respect for our family as we go through this difficult period."
The two held a commitment ceremony in Malibu, Calif., in 2003. Tammy Etheridge, 35, gave birth to twins - a son, Miller, and a daughter, Johnnie Rose - in 2006. The couple used an anonymous donor from a sperm bank.
The 48-year-old singer shares custody of daughter Bailey Jean and son Beckett with former partner Julie Cypher. Musician David Crosby was the sperm donor for the children, who were delivered by Cypher.
Melissa Etheridge was diagnosed with breast cancer in 2004.
