this really doesn;t seem like a baby monitor type of thing.

can you do it with a bunch of laptops and WIFI? Set the parental one to multicast using VLC (linux and Windows for sure) and the other laptops can receive the broadcast.

If you want, you could use an ATSC modulator (read expensive) and feed it to the TV's that already be in each room.

In terms of "talking back", I have no idea.

Or, find what kind of software those adult webcams use. It can essentially be two-way) with camera and possibly audio. Definitely typing works.