Generally speaking, you can usually take off about a quarter to a third of the top growth of most bushes without too much lasting damage although it will take a while for the plant to recover. The problem here is that you didn't provide a picture of how big the plants are now or their present shape so its not easy to say yes or no to your proposed trimming plan.
Certainly, you can always selectively trim errant stems, trunks, or branches that are not doing what you'd like them to do but major pruning should always be done with an eye toward minimal cutting at any one time rather than major pruning in one fell swoop.
Hope this helps.
Steve