WiFi range issues are commonly solved by adding additional "wireless access points (WAP)" at remote locations. Something like a
Netgear WN604 (10/100 wired, 802.11a/b/g/n wireless-150) or
Netgear WN802 (gigabit wired, wireless-300) are such devices, depending on your wired/wireless requirements at the remote locations.
You plug the WAP into some wired ethernet jack (provided either through an ethernet cable directly to the primary router, or maybe via a nearby PowerLine adapter if you don't have ethernet cable to the remote location). Then the WAP provides a second WiFi network on its own, along with providing additional wired ethernet jacks. It's like a second wired/wireless router but it is not actually a router. It's more like an "invisible extension" of the primary router, with all IP address handling and other network management for devices connected to the WAP (either wired or wireless) being done by the primary router. If you look at "attached devices" in the primary router, you'll see all devices gaining access through the WAP, just as if they'd been connected directly wired/wireless to the primary router.
The range of the WAP is very good, so even if there's no AC wall adapter in a room and no ethernet cable nearby, you can still use a PowerLine adapter in an adjacent room and place a WN604 or WN802 there in that other room, and you'll absolutely still get WiFi reception via the WAP where you want it. it's not quite as strong as the usual primary wireless routers, but it's still very very strong.
Should solve your problem. Note that the wired/wireless speed capability out of the WAP is 100% a function of the wired speed feeding the WAP. If you had the WAP connected via CAT5e or CAT6 cable to a gigabit router, you'd provide maximum wired/wireless speed from the WAP. But if you have CAT5 connection to the router, or you use a PowerLine adapter with low-speed capability, then clearly the WAP will also be similarly restricted on overall speed provided simultaneously to its wired/wireless clients. This is just common sense.