Try to use '127.0.0.1' instead of 'localhost'. If that doesn't work try to use a LAN setup with both of y'all on the same connection. (same internet connection)
Nice. I can do everything except the castle, that is.. for free content. Other builds and such I have to charge because of the amount of requests I get.
Okay, worldpainter doesn't support 1.13 yet so that really limits me in your request. I can try to use man-made underwater features (seaweed, coral, etc) but it's not going to be officially 1.13. According to the worldpainter Reddit forum the time for an update is unknown. I'm sorry.