I would probably suggest buying a cheap computer and a camera monitoring program. You will need hardwire IP cameras and inputs for the computer. They can be bought in kits. Hide it in a closet or safe (with proper cooling) and run cat 5 through the attic. Don't have a suggestion as to which one because I've only done commercial work and haven't researched it. I think that wireless is still too expensive for residential applications and the video quality isn't fantastic. Quality dedicated hardwired DVR's start at about $500, but I'm sure someone will be along to sing the praises of the harbor freight systems. When it comes to camera systems, quality is key. That said, I never recommend interior cameras in living spaces for obvious reasons. I'd prefer not to have video out there anywhere of me scratching my nuts while walking down the hallway.