It is a grammatically correct phrase, but it's incomplete. To make sense, you need to add a word after "ninteyaannu" specifying the relationship. For example:
* Njan ennum ninteyaannu makkal - I am your child.
* Njan ennum ninteyaannu snehithan - I am your friend.
* Njan ennum ninteyaannu bharttaavu - I am your husband.
* Njan ennum ninteyaannu bharya - I am your wife.
The phrase can be used to express various relationships, depending on the word you add after "ninteyaannu."