How to configure routing for multiple internet access

i have a RPI with 4 network interfaces that is used as a gateway/router eth0 (connected to internet throught local network) IP obtained by DHCP eth1 (used to connect specific devices) serving IP by DHCP server on 192.168.69.0/24 wlan0 hotspot serving IP by DHCP server on 192.168.125.0/24 wwan0 or ppp0 (4G/LTE modem) if eth0 is connected, traffic should goes troughth it else it should go throughth wwan0/ppp0 eth0 can be used to access RPI hosted HTTP SSH server wlan0 can acces RPI hosted HTTP server only eth1 devices can acces internet throughth eth0 or wwan0/ppp0 wwam0 can be used to access RP

Question by Eric Bouxirot on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.