Hi, I'm Pete. Welcome to JustAnswer! I'm reviewing your question now, and will post back with your reply ASAP.
Have you tried connecting to a different wifi network, e.g. a neighbor's or at a library?
If the Kindle device won't connect to any wifi network at any location then it has an internal fault and will need to be returned to Amazon.
Can you go out and try a different wifi network, e.g. a neighbor's or at a library, or Starbucks or some other public wifi?
If the Kindles still won't connect to any wifi than they have a fault.