You could look into MOCA adapters if the house has existing coaxial cable installed through walls for an old cable TV system. Plug an extra access point or two in and connect back to your main router via a few sets of adapters. It can cost a bit up front but it’s pretty reliable and if you buy old used 2.0 models you can save some money. (Just make sure they’re the same manufacturer)

Otherwise your options would be power line adapters to access points (bad, lots of chance for interference, neighbors adding a heavy appliance could break it).

Or nicer extending units located more closely together though if your walls are masonry or brick that may not help.

Also, inelegant and I hate to mention it but you could buy long, flat Ethernet cables, run them along the baseboards with the special retaining staples and connect that way to access points, though it does require space of a few cm door clearance in every doorway it has to traverse. Also flat cables technically violate Ethernet spec for preventing interference but in most single family homes interfere isn’t a big issue away from power supplies and runs so it would probably be okayish.