BLOCKCHAIN API (RBF FIX)

Hello Everyone, We are using blockchain as our payment service but blockchain doesn't support RBF i.e Replace by fee So our system is vulnerable to double spend attack or 51% attack Well , we have prevented it using minimum one confirmation for lower amounts But for one confirmation sometimes it takes 1-2 hrs. We want to let user balance auto update as they pay to address but by checking the RBF (false ) approved and RBF(true)wait for one confirmation. We want someone to build api for RBF checking and spent and unspent checking If anyone has knowledge about all this do bid on our project.