1) Yes, you will need to explain in LOE and also submit a notarized gift deed from your father. This will account for the difference between your current and average 6 months balance.
2) The letter showing 6 months balance is a standard requirement. See instructions below:
"Document requirements
The applicant should provide an official letter(s) from one or more financial institutions that lists all current bank and investment accounts as well as outstanding debts, such as credit card debts and loans.
o The letter(s) must be printed on the letterhead of the financial institution and must include the applicant’s name, the contact information of the financial institution (address, telephone number and email address), the account numbers, the date each account was opened and the current balance of each account as well as the average balance for the past six months.
Other documents may also be requested, as necessary."
All the best.