@JC-Corc 

If I understand well, everything works well when a device is close to any of the 3 Decos, but you have "dead zone" inside your house, where no device is working.  Is that correct?

Did you disable the wifi of your modem?

How are the satellite Deco connected to the main Deco?  By wifi?

Did you try moving the second Deco downstairs closer to the main Deco, instead as on the opposite side of the house?

  @yves_b 

If I understand well, everything works well when a device is close to any of the 3 Decos, but you have "dead zone" inside your house, where no device is working.  Is that correct?

Not quite - All devices work great in the room or close to the room with the main deco.  where the other hubs are (which are connected wirelessly to the main hub) our devices will connect briefly, then drop wi-fi within 5-30 minutes or so.  Then we cannot connect back to wi-fi from those areas.  I can be on top of the hub in another part of the house and it will not connect until I get back to the main deco where it's hard wired.  However, on the deco app, all are shown with full 3 wi-fi bars, and STRONG connections all leading back to the base.  I can also put an ethernet cord to either of the two decos and plug in my computer and it works fine that way....while the deco is only connected wirelessly to the main deco.

Did you disable the wifi of your modem? - No

How are the satellite Deco connected to the main Deco?  By wifi? Yes

Did you try moving the second Deco downstairs closer to the main Deco, instead as on the opposite side of the house?  Yes - we have tried rearranging all different ways.  But the same issue seems to happen.  Anytime the devices connect to a satellite/hub device...they are good for a couple minutes, then drop.  Then can't reconnect.

  @JC-Corc 

I suggest disabling the wifi on your modem, or, at a minimum, ensure it has not the same name as the wifi of your Deco.

Thank you so much for your replies  @yves_b 

Interesting...I have not had this suggestion yet.  Thank you for opening my eyes to another possible solution.

Our router is the Arris SB8200 Surfboard.  I'm not honestly sure if it is a modem/router all in one?  And I'm not srue how to turn the wifi off?  The unit itself doesn't have a switch...I assume I will have to log in to somewhere to check this??  (Can you tell I'm NOT that techy)

I only see the modem currently when I log into Xfinity.  I'm guessing I don't turn off the wifi there.

I did get another suggestion from TP-Link tech support and they suggested to turn on our guest wifi.  So I have that turned on now and am testing out the connection to that from various devices.  

For one, my printer actually now connects to the guest wifi, but I could not connect to it successfully to the main wifi even after successfully seeing it and putting in password.  (Different settings on both with may be why)

I also have an older computer that cannot see the wifi (main or guest) at all, even after updating all the drivers and entire computer.  So, I can't figure that one out either.

So...I will look into turning off the wifi next once I figure that out, and circle back.

THANK you for being so helpful.  I appreciate any and all suggestions.