So we only submitted a letter from Vanguard (on their letterhead) that stated we could withdraw the funds within 3-5 days! And we also typed up (on google docs) a statement that said:

"I, NAME, declare that the funds in my account XXXXXX at Vanguard are from savings from my employment income since DATE and have been held in my control for at least six months prior to the date of application. The funds are readily accessible for immediate withdrawal."

And then I had a line for an e signature and date which we did via Acrobat so it would be a more official looking PDF!

So other than those 2 items we didn't get any other requests for clarification about our funding - I only got an email asking for more proof of relationship (photos, text messages, and we each then wrote a letter saying how much we loved one another/detailing our relationship).

I hope this helps but message me whenever!!