Linux route different networks to local host

I want to build a Gateway with three Network Interfaces on a Linux board. I want to use eth0 wlan0 and usb0.

Connman manage eth0 and wifi, only one is active eth0 is preferred. So only one of the Connection is used. usb0 is not managed by connman, the Interface is en/disabled via an external Trigger. My Problem is, on the board runs a flask webserver, which should be reachable over all Interfaces.

usb0 provides a dhcp Server for the connected Client, eth0 and wlan0 are configured as dhcp Client. I want to reach the webserver on following ways:

- usb0 with the 192.168.2.1 (dhcp Server range 192.168.2.10 to 192.168.2.20)
- eth0 and wlan0 via the dhcp client address on each interface.