Thanks for the feedback!
Multiplayer works when I tested it, so hopefully it works for everyone else as well.
I will make it more obvious that the castle placement locations are intractable.
I definitely think this game needs more tutorialization and plan to add either a dedicated tutorial or a set of contextual popup hints pointing things out to you on your first time. But I think is that its best to get things as intuitive and learnable as possible with good UI/UX/tooltips etc first then add in the heavy handed tutorial elements after. But I think now is the time to start on the more heavy handed teaching.