In this simple setup, just use wds between AP 1 and two.
HotspostGW- Radio1 (wds) - Radio2 - Radio 3.
HotspotGW ether3 as hotspot Interface. Connect this to Radio1.
Then make a bridge at radio1 and put ether1 to bridge. Set AP as AP-bridge, and wds-mode to dynamic. Default bridge - bridge (dont put wlan Interface, just ether1 and wds interface)
Put radio2 as station-wds, and make a bridge. put wlan Interface and Ethernet to bridge.
Radio3, create new bridge, and put Ethernet and wlan Interface to bridge.