We did this with a single family that I converted to a 4plex. It was a large compartmentalized home. It had an upstairs game room with kitchenette and a bathroom. I was able to turn that into a studio by enclosing the stairway from the main house and building an exterior stairway and deck. It had an attached pool house type of area that also had a kitchenette and bathroom. I was able to turn the halway leading from the main house into the owner's closet by framing and sheetrocking one side. We created a full kitchen out of the kitchenette, walled off the open main space to give it an actual bedroom and living room area and we filled in the pool.(liablity) This gave us a true 1 bedroom 1 bath apartment and left the main house a 2 bedroom 1 bath. Lastly it had a carport area and about a car and 1/2 size garage all under the same roof. Actually under half the studio apt. I enclosed the carport area making that the bedroom and bathroom. Required a rear flush toilet in order to tie into the sewer system in the adjacent apartment wall which saved me from having to bust into the slab. The open garage area was transformed into the living room and kitchen open concept with a nice kitchen island. All apartments except the main house is heated and cooled with individual mini-splits with the main house left with the original central air and heat.
Sorry... That's a lot! LOL I kind of got carried away because I'm proud of the place. It's a cash cow as a STR and MTR now!
So, what we did with the WiFi is use Deco Mesh WiFi system. We placed the router in a locked owner's closet. I had to run an electrical outlet to that closet for power along with an Ethernet jack. I also ran a cat5 cable from that jack to the farthest apartment to the other side of the 4plex. Again, terminating the Cat5 cable to a jack in that apartment. Luckily all of that was accessible through the attic. In that farthest apartment we used the Cat5 cable to hardwire to one of the Mesh extenders. That covered the 4plex on both ends with the fastest signal. The other two apartments we just used the mesh extenders wirelessly as they were basically in between the two hardwired apartment's WiFi.
I hope this helps. We've been running like this for a year now with zero issues and everyone seems to love the WiFi speed. (AirBnB)
I hope this helps. Here is a link to what I am talking about just in case you're like me and know zero about this technology stuff. Because trust me.. Up until trying to figure out exactly what your're trying to figure out, I knew absolutely nothing about it.
Amazon.com: TP-Link Deco Mesh WiFi System (Deco S4) – Up to 5,500 Sq.ft. Coverage, Replaces WiFi Router and Extender, Gigabit Ports, Works with Alexa, 3-pack