Barb,
I see no reason why you can't prune these trees. As always, care and proper precautions must be followed in order to ensure that proper pruning techniques are employed. Furthermore, I always advocate dormant season pruning. Some people say whenever the pruning saw is sharp is a good time to prune trees - I personally do not subscribe to that point of view.
Several excellent publications regarding pruning basics include...
http://www.na.fs.fed.us/spfo/pubs/howtos/ht_prune/prun001.htm
http://www.ces.purdue.edu/extmedia/FNR/FNR-215.pdf
If you are not comfortable pruning these trees yourselves, then contact a local certified arborist from the yellow pages to do the work for you.
Hope this helped!