Don’t confuse “5G” with “5 GHz”.  They are not the same; they happen to have similar names.  Your 2.4 GHz devices will probably connect to the gateway’s Wi-Fi network, which by default broadcasts both 5 GHz and 2.4 GHz in your home. 

If you are having trouble getting them connected, post here again, and I or another helper will try to assist you.