clarification:
If your LNBs will work okay on 12 volts (probably good enough to get started), you're done.
A 4x8 multiswitch has eight
outputs.
The four inputs normally would hook to two, double-output LNBs.
... or maybe two LNBs on a feedhorn (one for V, one for H).
In your case, you could use four independent LNBs, one on each dish.
Now, you did say you had LNBs, not LNBFs, so if this is correct, each LNB will get one polarity (H or V) only.
But if you have the voltage-controlled LNBFs, now's the time to speak up.
'Cause that's a whole different situation.
Please see the link above into the Switch FAQ.
It'll show one way to hook up multiple LNBs or LNBFs.