Can I differentiate between 2.4 and 5 on MK63-100NAS

I have 4 teenagers and the six of us have been using the Nighthawk Mesh system for going on a year soon.   I've been very happy with the speed and reliability of the system as a whole.  We share 1Gbps between us.

We bought the nighthawk last year -when all of us are at home for work an school.  I have the mother and five satellites.

We have one large screen television from 2016 which requires a chromecast, and one from 2019 that does not.   

I have purchased a number of smart plugs before Christmas

what I notice is that the smart plugs only connect at 2.4, and the chromecast connects at 2.4.

The only way that I can get the smart plugs set up is to go out to my car in the driveway - turn off my wifi, and turn it back on.   With the walls of the house and car, it seems then my phone will connect at 2.4 and not 5.   then I can set up the smart plugs.  Once a smart plug is set up, then I don't have to worry about the connection on that particular plug.

The chromecast, however is more annoying.  When I try to connect to HBOMax or Hulu, the chromecast signal often does not show up on the app.   It seems that if I go outside to the car and reset the Wifi on my phone - so I connect at 2.4, then I am able to see the chromecast.  (My chromecast is from about the same age as the tv (2016).  

Is this the way all of this is supposed to work?  Is there a way to differentiate between the 2.4 and 5 signals, so that I can eaily make sure that I connect at 2.4?   Or is there a better way?

thank you in advance for enlightening me.