If WAN 1 is working, WAN 2 should indeed work with the same settings. Maybe you can check the firmware on the TP-LINK website, if there is a new one to upgrade, it’s worth a try.

the static IP address is used to match the IP of the Printer Sever, this is only temporary, so, do not worry. You may find the instruction on the TP-LINK official website:...

You’d better double check WAN port 2 is enabled, and working properly. After that, do the DDNS settings again. Are both DDNS accounts working fine? You know, they should be successfully set up, then...