To calculate the minimum flood insurance per the regulation for multiple structures, is (1) the lowest of the three calculated per building and then added together to get the total minimum flood insurance required or (2) are all buildings values added together and then the lowest of the three determined?

This might be helpful. Credit to Dan Perfull!!

https://www.bankersonline.com/tools/151072

Assuming all three buildings are in the flood zone and none meet the additional structure exemption, the minimum will be the lesser of:
1) the loan amount (can split the amount anyway between the three buildings, but all three must have a policy),
2) the sum of the insurable value of each building (will need policy in the amount of the insurable value for each building), or
3) the maximum available through NFIP ($250,000 for each residential building and $500,000 for each multi-family or non-residential building).