i am a total noob, i my head it would be best to setup a vpn server at the openwrt router -> lan1
and to connect, first use the vpn from wan to lan2 and than the vpn to lan1 over the openwrt.
to be honest that is my first time trying something like that and i am fighting with all the new stuff in the linux world (switched from windows 5 days ago, and flashed my xiaomi router).
thanks for your help!
Do i need to open any ports?
I have no access to the hardware of the wan->lan2 vpn, so i cant change any settings there.
There are plenty of Free Software VNC servers and clients. GNOME which the default Ubuntu user interface is built on has a VNC server built in, go to settings > sharing > screen sharing
for clients, I think Vinagre is default for GNOME.
yes, in your example config, for the router itself, you need to accept INPUT on WAN for ports 22,23,24 and whatever ports you forward for VNC (note, VNC by itself doesn't encrypt its traffic, so you're really best off to tunnel the VNC over the ssh connection, which Vinagre can set up for you (in its connect dialog "use ..... as a ssh tunnel" or some such thing). In that case, you just only forward the ssh ports.
BTW: I would recommend to use different ports for all of these, try 1322 1323 1324, this way you're not interfering with ssh itself on the router.