mate I am no networking guru, just bumble along until it works, when it doesn't work go back and start again.
Have gone back into what is actually five softether installations, 1 x VM server only, 2 x standalone server only, 2 x standalone server/gateway. Softether install is as per wiki.
Of the two in server only mode, both with DHCP disabled, both with ports forwarded to localhost, both modem/routers have port forwarded to the sme ip - 1 has to have the virtual nat enabled to work the other does not, the only difference between the two is the brand of modem-router. 1 x TPlink, 1 x Billion, the billion is a 7700N R2 needs the virtual nat.
Theres some food for thought for you bosco555