childs custody ? to Childs father or to childs mother ?

childs custody ? to Childs father or to childs mother ? 1) twins female Childs was born by test tube baby treatment through donar egg and childs father original sperm 2) after 4 yrs, now childs both parents father and mother wants to seperate from each other mutually due to personal and financial problem and misunderstanding amoung them 3) but childs Father is refusing to give the children to mother , stating that childs does not belong to mother, as the childs were not born with the mothers original embryo egg, it was an donor egg and the original sperm belongs to childs father 4) thus childs father is not willing to hand over the children to its mothers 5)So, please suggest, who will get the custody of the twins female childs between father or mother 6) how to take the custody of the twins female childs to mother without applying for divorce or we have apply for divorce to get the children Custody