There are as many solutions to this problem as there are people doing it. In my case, I would put a radio controlled switch at each location. Many of these report the status of the switch and some of them report the power usage. Being me, I would chose something with XBee or ZigBee mesh networking so I could expand it later.
Since you have two lights and four switches, you probably have two, two way switches for each light; one to turn it on as you come in and one on the other side as you go out (so you don’t have to go back). That would mean a SPDT relay to handle the various possibilities on one of the switches. Or, you can make one of the switches actually control the lights and the other switch just send a signal to the first switch to command it.
You could bite the bullet and wire the lights to a central controller and make all the switches radios that tell the controller which light to turn on. This is the most versatile method since you can reprogram the system to do anything you want
What everyone tells you about powerline controls is absolutely correct. You have to have a really quiet electrical system to make that work reliably and every motor, computer, switching power supply in the house will work to mess you up. Those were OK forty years ago, but they don’t work worth a darn today, unless you have massive capability for retries and control packet integrity.
Everyone thinks hard wired is the way to go. Someday you’ll want something where there are no wires. What happens when you forget and drive a nail through one of them? The wire gets eaten by ravenous bats that decided to populate your attic? Sure, radios die, but they’re simple to replace; wires are tougher.
If you want to go Wifi, there are a couple of switches that use UPnP over ethernet to announce their presence and allow you to control them. If you want to go ZigBee the choices are limited, but they exist. Z-wave switches are abundant, but the controllers are all proprietary (unless you want to go to a Raspberry Pi). Xbees running a simple text protocol are cheap, but you have to build your own stuff. Perhaps hook a relay to an XBee digital pin and put the entire thing in a wiring box next to the light; you could hook a switch to a digital pin to replace the wall switch. Then put the controller (an arduino) on a shelf somewhere.
But, you say, "the radio is much cheaper and works really well. That’s true, but what happens when you expand the system and the next radio just can’t make the hop from the wall of the garage through two interior walls to the shelf where you put the arduino? With XBees, this is simple, put a repeater in between them. With other radios, have a nice time writing your own packet forwarding code. Z-wave and ZigBee handle this well also. Wires don’t handle it at all, you have to run a new wire.
See what I mean about possible solutions? You’ll have to consider the future of this one room house into your plans.
