Duplex with 20% down for an investment property

[Kerry Arm]

Looking to possibly purchase a duplex as a rental property and looking for a lender that will allow 20% down and one mortgage in CT, anyone knows of any?

My second question some what ties into the first. Is there a reason why the seller would hint that they rather the buyer take two mortgages out to purchase their property?

Thanks in advance, all help would be greatly appreciated.