SNAT/DNAT 1:1 NAT with identical LANs

[jagrok]

I want to connect several LANs located on remote buildings
The central site is a server running OpenVPN
Each remote site also run OpenVpn in Clien mode.

1. The central site has only one public IP
2. Serveral remote sites are using networks 192.168.0.0/24
3. I cant/wont to modify LAN numbering
4. I want to control these networks via the client

I know that i need definie virtual LANs
I know thats works on dnat/snat

site A
192.168.20.0/24 real network
10.9.1.0/24 virtual network

site B
192.168.20.0/24 real network
10.9.2.0/24 virtual network

site C
192.168.20.0/24 real network
10.9.3.0/24 virtual network

site Server
Global IP
10.8.0.1 - virtual network
10.8.0.0/24 - assigned ips for remote computers not routers

So each site is seen to have a 10.9.x.0/24 LAN
When a VPN Client want to get access to 192.168.20.17 on site C its sending request to 10.9.3.17
If the same client want to get access to 192.168.20.1 on site A - main router its sending request to 10.9.1.1

Site A/B/C - cannot communicate together, only remote computers can do access to the choosen network.

Client A - 10.8.0.6 can connect only to site A and C
Client B - 10.8.0.12 can connect only to site A,B,C


I found some information how to do it on snat/dnat from but it`s really hard to find why it`s doesnt work.

I now that the OpenVPN from version 2.3 are included client-nat dnat/snat option

Is any body who can help me with setting this ?