Internet setup help! SOS!

Hey everyone, we’re running a small hospitality business with eight rental units. The house itself is about 7,000 square feet—a three-story build measuring roughly 22 by 7 meters. We’ve hit a massive wall because the Wi-Fi signal barely reaches anything in the building. We tried buying those cheap range extenders and similar gadgets, but honestly, they were a waste of money and didn't solve a thing. I'm looking for some advice on the best way to set this up properly. Are there specific high-powered systems out there actually capable of covering a footprint like this? Any help would be much appreciated. Thanks!

We don't actually know what kind of Mbps speeds you've signed up for with your ISP, so there’s no way to tell if it can even handle a crowd.
The only real way to blanket the whole area without running a massive mess of cables and gear through the building is to set up an AP (or maybe a couple on different channels) about 60 feet away from the site—somewhere where you have a clear line of sight to all the balconies. You'd need an outdoor AP with a beefy enough processor to juggle multiple users, plus some built-in directional antennas around 9dBi, then just run a UTP cable back to your home router. I'd let the contractor pick out the specific hardware.

ps: Honestly, skip those cheap range extenders. They act like repeaters that basically cut your speed in half, and since everyone ends up fighting for space on the same channel as the router and the users, the interference makes the whole thing pretty much useless.😢
It would be a smart move to make sure those WiFi APs are dual-band, supporting both 2.4 and 5GHz, since pretty much every smartphone and laptop out there uses both.

With eight apartments on the hook, I don't think any "DIY" hacks are going to cut it. You really need to bring in a pro to design and execute the whole setup if you want it done right.
The mistake happened way back during the initial build or renovation phase; they should have just run Ethernet cabling through every single unit from the jump.