@JamesSolomon 

Bring both Satellite Deco to the same room as Main Deco, place them about 3-6 feet (1-2 meters) from Main Deco. Check Signal Source on Satellite Deco.

Possible outcome:

A) You do not see 5GHz - you have defective Deco hardware;

B) You do see 5GHz - material your ceiling is made of does not allow 5GHz to penetrate it.

Example of Signal Source with 5GHz in it:

  @JamesSolomon 

Its also worth noting that 5ghz is a lot more susceptable to intereference when compared to 2.4ghz.  

You may find that the Deco has determined that 2.4ghz would give you a better experience in its current location vs 5ghz.     As mentioned above try moving one of them in the room with the main and see if this changes, if it does its likely signal issue. 

Something like WiFi Analyser for Android may help you see what you are reallly getting in the area of the 2nd and 3rd nodes.    If 5ghz is sitting around -70db or higher then its not going to be great for you, ideally you want -60 or lower when placing your deco nodes

Thanks everyone. I will try these two things out, and let you know if I still dont come right.