Ok try this. Set a static IP address of one of the access point to the lowest IP address available on the router and set and set the DHCP to auto.
On the other AP, set the IP to a static IP to the highest IP address available on the router and switch off DHCP.
Makes sure that both access points have the same SSID. Make sure the WPA-PSK key is the same.
If there are roaming settings, set them to high or aggressive.
(I haven't done this for a while so had to research to refresh on this as all the children have at last moved out :beaming_face_with_smiling_eyes: and I stopped doing it for clients).
Oh, and make sure each access point channels are not the same, overlapping channels usually interfere and cause confusion, I usually set them to 6 and 13.