We are making a blanket loan on two contiguous two family homes. The properties are in a flood zone. Should I require $250,000 each for a total coverage amount of $500,000 or is there a single loan limit of $250,000?.

You need to the lesser of the loan amount, the insurable values of the buildings - subject to the limit of $250,000 per building, or $500,000 which would be the two policies.