The account doesn't have to be in the name of the principal applicant, for our application all of the funds were in my wife' s account, my name wasn't on the account at all and I didn't have permission legally to use the account. She wrote a letter saying that she considered all of our money to be joint and that I had her full permission to use the money however I wanted, including for the purpose of our settlement funds. She also wrote that at no point in the future would I be expected to repay any of the money I used.
As to a joint account with your mother though...I don't think so, I think if its the accompanying spouse its different, I am no expert though, only know from our experience.
Hope this helps.