@techvic I don't know if you eventually got everything worked out, but at a high level, what needs to happen is the mobile clients @ site A have to know that site B's LAN is accessible thru the tunnel and site B needs to know that site A's remote access tunnel network is accessible thru the tunnel.
Also, assigned interfaces are not required to get this working. The routing is generated by OpenVPN behind the scenes based on the options provided in the GUI.
If your issue is resolved at this point, great. If not, I would start a new thread.