Under Configure -> WLAN, create two new WLAN Groups, call them 2g and 5g.
In each group, enable the SSIDs you want enabled in that band (eg. In your example. You would enable all 3 SSIDs in the 2G group and only enable your 2 older SSIDs in the 5G group)
Under Configure -> Access Points, edit the Default AP Group and set the correct WLAN Group on the respective radio (2Ghz Radio = 2G WLAN Group, 5Ghz Radio = 5G WLAN Group).
Remove all the overrides on the individual APs.