You cannot have two NFIP policies on the same property.
Your original thread from 2/25 goes into this in detail. The key comment is this:
"Yes. You would have to request them to increase it to cover your loan and add you as junior lien holder. You would fund the additional premium, recouping it from the borrower by charging it to their loan."
Some way, some how, you need the required insurance, and the insurance you force place must cover the borrower as well as the bank.