How to get marriage certificate without knowing our parents?

If marriage is already solemnized and you want to get marriage registered then,
A marriage which has already been solemnized can be registered either under the Hindu Marriage Act, 1955 or under the Special Marriage Act, 1954. The Hindu Marriage Act is applicable in cases where both husband and wife are Hindus, Buddhists, Jains or Sikhs or where they have converted into any of these religions. Where either of the husband or wife or both are not Hindus, Buddhists, Jains or Sikhs the marriage is registered under the Special Marriage Act, 1954.

The marriage which has already been solemnized can be got registered at the office of Sub-Divisional Magistrate in whose jurisdiction any of the husband or wife resides on any working day.

The following documents are required for registration:

1. Application form duly signed by both husband and wife.

2. Documentary evidence of date of birth of parties (Matriculation Certificate / Passport / Birth Certificate). 

3. Address proof of both the husband and wife. Adhaar card was being required for registration too.

4. Affidavit by both the parties stating place and date of marriage, date of birth, marital status at the time of marriage and nationality and that the parties are not related to each other within the prohibited degree of relationship as per Hindu Marriage Act or Special Marriage Act as the case may be. 

5. Two passport size photographs of both the parties and one marriage photograph.

6. Marriage invitation card, if available.

7. If marriage was solemnized in a religious place, a certificate from the priest is required who solemnized the marriage.

8. In case one of the parties belong to other than Hindu, Budhist, Jain and Sikh religions, a conversion certificate from the priest who solemnized the marriage(in case of Hindu Marriage Act).

9. Two witness with photographs and copy of their PAN Card.