Plug video into the sky box where it says "VCR/video". Make sure all 21 scart wires are connected (if its a good one you can unscrew its end and open up carefully). This lead will serve to switch the sky box over to the VCR to playback, when you press play on the video. It will also let you record sky channels via scart.
Then use another good scart cable between the tv and sky box.
DVD straight to the TV. If available, use 3phono wires for this. (red white and yellow)
Aerial goes from aerial - sky - video - tv (for full functionality)