OCI and PIO cards

[cunha]

Four children born in Canada and have Canadian passports. Three are adults over 18 years. 4th child is 16 . Can adult children apply for OCI on their own? If so, what are the documentation requirements? They do not have their own Indian addresses as proof of residence in India. Both parents are PR Card holders in Canada and Indian nationals with Indian passports with Canadian address on passport. The Indian consulate have discontinued endorsing Indian addresses on passport.

I believe 4th child can be applied as minor for PIO card by parents. If so, what are the documentation requirements including proof of residence in India for the child and parents in India.

Can anyone shed some light please.