In a mutual divorce who keeps the custody of the child

Dear, My cousin bother, he is in mid of 30's. having kid about a year old. as of now he is separated from his wife and kid, they are planing to have mutual consent divorce. and would like to know about child custody rights after 5 years, and at 9 years. he is not interested in neither taking joint custody nor visiting rights until 9 years. he personally feels it may lead to one more addition in unresolved. I was insisting him to take full custody, after 5 years or earlier than that. because I feel, considering the kids future on her remarriage if so. what is your opinion based on your experience. what are the factors, should he consider as predominant terms. while drafting mutual divorce petition regards