They will not allow it from 3 months. It should be at least 6 months. Just wait for another 3 months then.
As far as I know, only Attested Marriage Contract from your embassy is enough and not all should be attested. And if you can manage to process all your documents, do it.
I applied my child's sponsorship this August 2014 and I only attested my marriage certificate from my country's embassy. I got approved within 3 days and visa stamping within a day.