Proper organization of a Wi-Fi network?

Question

Computer networks

There are 2 floors in the building (3 and 4)
There are 3 Cisco WAP4410N APs
Now organized as follows:
On the 3rd floor under the false ceiling in 3 spaced places, there are APs, all transmit the same SSID, Wireless Isolation: (between SSID) is disabled.
Checked the monitor, took the most unoccupied channel (it seems the 5th)
People complain that it does not work very stably. How to improve / redo?

Answer 1

As I understand it, all access points work on the same channel.
There is a discussion
In case of roaming, all settings except channels should be left identical.

Answer 2

Yes, and check if there is a kitchen room with microwaves nearby) Everyone knows about radiation, but when installing Wi-Fi, for some reason, many people forget about it)