You need to read up on purpose and reasons for using both bands. I use both bands, 5G was developed to be a faster speed signal necessary for streaming video. it has less range, though. 2.4G is the earlier wireless signal, and it has greater range but is less suitable for video stream. So,
Go back to two SSIDS (named XXX_5G and XXX_2.4G to differentiate them. Put any video streaming devices such as Show on 5G and phones and tables; anything that can stream video on 5G. Put Echos, etc (any audio only devices) on 2,4G. This is what I do.
You sound like your 5G is out of range for some devices, so you may end up having all on 2.4G.
The only way to extend range is to use a range extender, but that can be tricky to setup for sume. I have one for each band.