Would an external wifi adapter and/or antenna help? Or one of those wifi signal boosters you plug into an electrical outlet? Any recommendations? I've tried all the advice where you reboot your router, clear obstructions, etc.
Also, someone in my house has a gazillion device connected to the wifi, but they're off most of the time. Does the fact they're connected slow down the signal at all, or only if they're on and actively connected?
Devices that are off won't slow down the connection. However, if you are near enough to other wifi networks, you may get some help by changing your router's wifi channel. This will require some trial and error testing. Is your connection slow when you are fairly near the router? Are you seeing a strong signal when in a normal (slow) location? If so, an extender won't help.