Your challenge is handling the throughput demands with channel contention. Your devices are all close enough that you need to assume they are all potential interferers to each other so you will need to use a protocol that is robust to this - probably using some sort of coordination between devices to ensure they all take a fair slice of the channel.
The WiFi we know and use now also share the 2.4 GHz frequency range with a lot of other technologies and applications which might interfere. If we have a look on the list of 2.4 GHz radio usage, a couple of items are there beside WiFi.
Many cordless telephones and baby monitors in the United States and Canada use the 2.4GHz frequency, the same frequency at ...
There are two aspects to this regulatory regime which you need to understand the impact of.
Accept interference. One of the constraints of an amateur license is that continuous transmission is restricted. The underlying assumption is of a 2-way human-to-human conversation, so transmit time is unlikely to be longer than 15 minutes continuous. Beacons and ...
One Access Point for 250m2 and 3 floors, seems to stretch WiFi a bit.
It depends on the material in the building, surrounding interference and antenna.
To give a answer, one should do a survey and measurements on site.
A Guesstimate would be probably not.
Your best bet is DASH7.
It's pretty unknown even among nerds, but if you want a solid industrial stack, DASH7 it is. In case you haven't heard of DASH7 before, it's the official IoT standard of all NATO member countries and the Department of Defense:
DASH7 has been mandated by the U.S. Department of Defense (DoD) and NATO alliance.
The beauty of ...