We have a loan on a mobile home park. We also have several mobile homes that are taken as collateral. This park and all mobile homes are located in a Special Flood Hazard Area. All of the mobile homes do not have flood insurance however the ones that do have coverage have enough to cover our loan amount which is the lesser of the 3 items to consider. Is it necessary for us to require flood insurance on the other MH's that do not have coverage?

Yes. Every structure needs to have a policy.

But only the homes that are owned by the park and therefore serve as your collateral. If any of them are owned by the occupant, they are not your collateral.