It "should" work correctly configured without the nat on your server. What is likely happening is the router will only NAT addresses from the main lan subnet. Not sure what you do about this since many routers have this issue.
When you use the NAT configuration on your server then you have the standard port forwarding issue.
The only way I could see to fix it would be to use a 1-1 nat for all your devices on lan2 rather than natting everything to a single address. You would likely have to increase the size of your lan1 subnet.