Are they close enough to the router? Do you get good WiFi signal where they are?
I had to get a WiFi extender for my Pixie to work, and it’s right outside my house. I plugged an extender into the shared wall, connected it to my router (make sure your extender requires a password), and now everything is working properly. It even made cell phone coverage in my house go up (WiFi calling)
Let me know if you have questions. I don’t want to seem like I’m selling a certain brand extender, which is why I didn’t tell you what I used. :)