How to set Ubuntu 2 interface to LAN and Proxy Internet

I have 2 interface ens3-192.168.100.10 and ens8-10.100.0.10. Both get via dhcp. ens3 is for lan access and ens8 is for proxy to internet and to run apt update. Problem is now I have to 2 default routes and both have same metric 100 but it make both networks not stable. I tried changed so that Lan/ens3 will be default by making ens3 higher metric. The ens3 network stable but I could not access internet and made any apt update/install. I can ping my proxy using source -I ens8. How to change the route, please advise and help further. Thank you for your attention and great help.

Updated1: I did set static of each interface and the route become something like below; default via 10.100.0.1 dev ens8 proto static default via 192.168.100.1 dev ens3 proto static

  ---Now I can access internet and update apt but I cannot reach my 
  lan. Still no idea.

Updated2: This is the routes

  default via 10.100.0.1 dev ens8 proto static metric 200
  10.100.0.0/24 dev ens8 proto kernel scope link src 10.100.0.10
  192.168.100.0/24 dev ens3 proto kernel scope link src 
  192.168.0.10

internet/update works and from the server and i can ping to lan. The problem now from my lan cannot reach (ssh) to this server.

It sounds like your dhcp server on ens3 is misconfigured, if it is offering a default route but should not be used for the Internet.

However, netplan has a complete set of options for overriding wrong dhcp settings. If the only network you need to reach on the LAN interface is a single directly-connected subnet, you can use the following to ignore all dhcp-provided routes (including the default route):

network:
  version: 2
  ethernets:
    ens3:
      dhcp4: true
      dhcp4-overrides:
        use-routes: false
    ens8:
      dhcp4: true

If you have other routes you need on ens3, you can instead give them a higher metric, so that the default route from ens8 will be used in preference over the one on ens3:

network:
  version: 2
  ethernets:
    ens3:
      dhcp4: true
      dhcp4-overrides:
        route-metric: 300
    ens8:
      dhcp4: true

https://netplan.readthedocs.io/en/stable/netplan-yaml/#dhcp-overrides