That explanation makes no sense whatsoever. Having an external web server for a Hotspot has nothing to do with duplicate IP ranges (which is something you simply shouldn't do).
Please provide a network diagram, and a detailed explanation of what you're trying to do. By that I mean the goal you're trying to accomplish, not how you think you'd have to go about it to get there.
Specific answers require specific questions. When in doubt, post the output of "/ip address print detail", "/ip route print detail", "/interface print detail", "/ip firewall export", and an accurate network diagram.