Will NPCs spawn on the second floor? I was going to copy the second floor and tower up. Will they be able to walk up those stairs? If not, what do i need to do to fix it? (The house on the left) Please respond.
It should, if you're not sure, there's a house icon that you can pick it and see if it's suitable or not. It's near the helmets icon.
All housings in that pic are suitable, except the first floor of the middle building. It needs a chair.
The housing query (the '?') isn't always reliable. The best way to tell is to try to assign an already-spawned NPC to it (like the Guide, or your Merchant there); click on the house icon, then the Guide badge, then click on the house in question. If you can't place the badge, there's something wrong with the house. But that one on the left looks ok to me as well. Please be patient, and please don't multi-post like that. This isn't a chat room, and immediate responses shouldn't be expected. Welcome to the forum, and please read the rules when you get a chance.