Please provide an explanation and evidence of difference in surnames

Hi Anil,
Hope you are fine.

I have received Request for more Information from AUS Authorities. We did not change the last name of my wife to match my last name on her passport. Her 10th 12th Graduation marksheets are also with old name.

However, in the marriage certificate her last name was changed. My daughter’s passport also has her changed last name.

Request for more evidence for my wife states" Please provide an explanation and evidence of difference in surnames".

What should I do in this case?

Can you share the screen shot of the CO letter? They must have mentioned how to prove it too.