How Do We Get Custody

My question involves a child custody case from the State of: Kansas and California
My Husband has 2 childern that live in California with there mother they was living with there grandma and grandpa intill last week she lives in a 1 bed room ap with 3 kids and no job. Me and my husband are wanting to get custody of his Daughters but they live in California and we live in Kansas and we are not sure how we go about in getting custody of them. and now that the mother has the childern my husband will not get to see or talk to them

Does your husband have a visitation order?

Also, no matter what happens with father and children, you'll be a legal stranger to the children unless mom's parental rights are terminated and you legally adopt them. So DAD can seek custody, but you won't legally be a part of that order if he's successful.

In order to BE successful in a quest for a change in primary custody, either (a) mom needs to agree to it, or (b) mom needs to be proven unfit (and no, being unemployed and living with 3 kids in a 1 bedroom isn't close), or (c) demonstrate to the court that some substantial change has occurred in the children's lives which is both related to mom having custody and which could be alleviated by a change in custody. In other words, things like "the children are too young to be left alone while mom works, but she frequently leaves them unsupervised", or "mom's living situation is so unstable that the children haven't been able to attend school", etc.