The OP could probably use a series of these:
Only £17.57 each from here:
http://cpc.farnell.com/AV17636/audio...nics-prism-slv
It includes connections for Scart and RF out (which, intriguingly, it labels as RF loop-thru) and the power consumption is a measily 6.2W (active) / 5.5W (standby). User manual, such as it is, available here:
http://www.remote-controls-shop.co.u...splay=file.pdf
If the loop-thru doesn't work then you could use a distribution amp to divide the signal from the aerial to all the tuners and a splitter, wired in reverse, to combine all the outputs.
I'd still be tempted to ditch the VCRs and replace them with PVRs. More channels and more versatile. However, it may be difficult to find one with an RF output.
Some cheap options here:
http://www.tvonics.com/