I'm not sure if he can actually feel the speed, my dad can't tell if he is on 4G or unifi. but what you can do for sure, is to make all the staff happy with the reliability.

AP I would recommend EAP225, really cheap and robust AP. worst case conditions (3 walls) was faster and stabler than my AC86U. It comes with it's own poe injector as well.

If you are willing to spend more, I would recommend EAP660, a high-density AP, which is on the luxurious side. I have several friends use it and couldn't turn back due to its robustness even with inteferences from neighbours.

Router can consider mikrotik. hex or ax3. rb5009 if u r willing to spend.

ax3 comes with its own wifi so u can put other APs further away. rb5009 poe doesn't work with EAP225 unless you use a 24v adapter, which make rb5009 lost its POE+ functionality (48V).

Cheap setup
Stock router
Managed switch
Numerous EAP225.

Moderate setup
Hex/ax3
Managed switch
EAP660 for workers+guest and EAP225 for staff (i assume it is a smaller space and less devices)

OR

ER7212PC
EAP660 + EAP225 if needed

More luxurious setup
rb5009 POE
EAP660*2