Correct. You just need to make sure the coax lines are connected in a parallel fashion (does this make sense to you? "Parallel" is a word from electromagnetism I believe.)
In your house, you should find a splitter or splitters that connect all the coax wires together. For example, like this:
You just need to make sure the WCB3000N's coax line and three STB boxes' coax lines are connected together, either directly or through splitters. Technically, you can just plug in the WCB3000N to a random coax outlet and they should just work if every coax outlets are connected together.