This is taken from California Child Custody Law and Procedures
http://www.kinseylaw.com/clientserv2/famlawservices/childcustody/childcustody.html
5. Separation Of Siblings: California policy affords strong protection to sibling relationships. Absent compelling circumstances, such as extraordinary emotional, medical or educational need, an order separating siblings between custodial households ordinarily will be reversed as detrimental to the children's best interest. [Marriage of Williams (2001) 88 Cal.App.4th 808, 814-815, 105 Cal.Rptr.2d 923, 927-998]
6. Child's Wishes: The court must "consider" and give "due weight" to the wishes of children who are of "sufficient age and capacity to reason so as to form an intelligent preference as to custody." [Ca Fam § 3042(a); see also Ca Fam § 3030(c)(1)].