US Immigration from Nepal

I'm helping out with my sibling's application for citizenship. Him and his wife have been a Permanent Resident since 2012. They are applying on the basis of 5 year residency.

They are submitting scans of their PR cards and marriage certificate, as it is requested on the application. However, they do have an additional evidences section.

What would be the best additional evidences to be submitted with the online application?

Thanks in advance! :)

We are a few weeks away from submitting our i-751. The problem is we will be out of the country for two months this summer, before moving to another address (where we have already signed the lease). We were thinking of using my wife's parents' address in a different state for the summer. Can we also add next year's address when we note the list of addresses in the additional information section?

Also, related question, is traveling internationally for two months right after submitting the i-751 going to be an issue? We will be back 3 weeks before the green card expires.

Hi, I have my interview coming up. Do I need to have the Affidavit of Support Document originally signed by my spouse with me during my interview at embassy? Or will the photocopy suffice?

Thanks in advance.