If you do not have a marriage certificate then you can use a marriage affidavit to add your wife as dependant in your medical insurance cover. Her is how get marriage affidavit.
For children below 18 years you need to provide a birth certificate.
Children between18 to 26 years can only be added if they are still in school. In such case, you should provide your child’s school ID or letter from school principal.
Disabled children can be added without any limit in age as long as you provide a disability card.