I assume you already enabled Softphone/BYOD option in vPanel. Also, I don't believe you can have two lines with BYOD option. I think the two line option is supported only with provisioned ATA.

If you have a good router with SIP ALG, then you don't need STUN server. Otherwise you might need to set the STUN server. I believe 174.37.45.134 is the stun server on VOIPo network.

When we used Grandstream ATA and set "Use Random Ports", then it will not use the port range you set. You might want to set that to No and see if that makes a difference.