perhaps already done, but a few items to check
remove all reservations from the devices you wish to have on a separate (new SSID) network
on the device itself remove or 'forget' the previous network's SSID
a couple of my devices were very stubborn to 'move'. when i defined the new SSID i allocated the full network, but only allowed a subrange of addresses for dhcp. i assigned a fixed address for 24hours (my dhcp renew time) then returned them to automatic. after that, they all played nice and connected where i wanted them to connect.on the device itself remove or 'forget' the previous network's SSID