AOS I-485 for spouse: Marriage certificate not available

[tejasm]

I am filing for AOS I-485 for my spouse and me. We were married in India in a religious ceremony over 6 years ago, but have been unable to get a marriage certificate due to certain procedural roadblocks. 
However, we have compelling evidence of being married, including:

1. Filing taxes jointly for 6 years

2. Joint ownership of a home (and joint bank accounts)

3. A child together 

4. Passports that list each other as the spouse

We spoke to an immigration lawyer who advised us to get a US Marriage Certificate, which we are in the process of procuring. However, the date on the marriage certificate will be close to the date of filing for AOS.

Would you still recommend getting one and furnishing that as evidence?

Are there any other documents (affidavits from our parents, for example) that could be acceptable for this purpose? 
 

thanks!