There are several issues here that can't really be addressed without the lease. For one thing, many consumer protections that apply to larger mortgage lenders do not apply to private citizens selling their own homes, or private groups providing "hard money."
Assuming the bank is a regulated institution and the real estate agent is a licensed professional, there are a few issues that may indicate fraud.
1. No one with who stands to benefit from a purchase transaction is allowed to contribute to the down payment. Seller, lender or real estate agent, for instance.
2. Borrowing your down payment is extremely iffy. Some programs allow it from family members, employers or charitable groups and you must disclose it. If you borrow elsewhere prior to buying, you have to disclose the fact that you borrowed your down payment on your loan application. Most programs forbid borrowing a down payment except in extremely limited circumstances, and the ones that allow it are usually government programs.
Try borrowing your down payment without disclosure and you'll likely get caught. The big deposit will also appear on your bank statements, and lenders are not blind or stupid. Maybe that's why you're being "encouraged" to use a certain bank by your real estate agent.
However, if you took a personal loan, say, a year ago, and stuck the money in your bank account, those funds eventually co-mingle with your other money and can't really be separated. You can say at that point your down payment is savings -- BUT you must also disclose the loan balance and monthly payment on your application.
3. No seller or agent can require that you use a certain institution to get a home loan. It is a red flag that they would even try.
4. A lease option is two separate transactions -- a lease, and a purchase. They are tricky and you should always have a lawyer vet them before signing. Many opportunities for fraud. And many lease-options are simply attempts to get around the due-on-sale clause in mortgages, which means homeowners who sell property to new buyers without paying off their current mortgage or disclosing the sale to the lender, which could call in the loan and perhaps force a foreclosure.
5. Does this pass the smell test? Real estate expert John T Reed puts it best, I believe:
"IN GENERAL, YOU SHOULD NEVER DO ANYTHING THAT CANNOT STAND THE FULL DISCLOSURE TEST. THAT IS, IF THE DEAL COULD NOT BE DONE IF EVERYONE INVOLVED, INCLUDING ALL THE LENDERS, KNEW EVERYTHING THAT WAS GOING ON, THE DEAL IS PROBABLY UNETHICAL AND ILLEGAL. THE TYPICAL LEASE-OPTION ACQUISITION CANNOT BE DONE UNLESS THE EXISTING LENDER IS KEPT N THE DARK ABOUT THE CHANGE IN CONTROL AND OCCUPANCY OF THE PROPERTY."
THE BOTTOM LINE HERE IS THAT BREAKING THE LAW OR A CONTRACT IS A SERIOUS THING.
You probably need a real estate lawyer NOW.