You may not transverse the two networks in that manner. IPSec prevents this type of behavior. IPSec encrypts packets from LAN 192.168.12.0/24 and sends them to device with LAN 192.168.10.0/24 to be...

On the TL-R600VPN IPSec Policy Settings Change PFS Group DH2 to Disabled/None and try your connection again.

Another question, when you wrote "I can connect a device and it would have access to the internet, but I can't see it from within the wireless network (192.168.0.x)." What did you mean you can't see...

You have done something wrong. Re-configure both Access Points with the same SSID Access Point upstairs use ip address 192.168.0.254 Access Point downstairs use ip address 192.168.0.253

Please provide a diagram or more detail about all network devices and connections to their respective ports on each of router and adsl modem.

Please include network diagram or more details about all devices including NAT, port forwarding and firewall position. Also what is your phase 2 parameters for your TL-R600VPN? (ex.pfs_group ?;...