The devices that are on the 2.4ghz signal atm can only support the 2.4 and cannot be split between the 5ghz.
I do know that each band wave no matter what the ghz output so 2.4 or 5. they will take a maximum of 32 devices.
I'm assuming though that because so much is used and its close to maxing out are the current devices fighting against eachother for the signal.
If this is the case will a MIMO router help. this will distribute the signal alot better but I think the mimo only affects 5ghz and not 2.4ghz signla but not totally sure.