Review their IEP's then give them some simple assesments to check their skill levels. I like [url]http://www.edhelper.com[/url] though you do need to pay a yearly fee to access most of their materials.
Once you've determined their skill levels, plan your scope and sequence for the year. Work out the order you will use to develop their skills (ie types of sentences, nouns, verbs, subject, predicate and so on) making sure to focus the program around their IEP goals.
From there it's a matter of planning lessons, taking things one step at a time, doing lots of review and practice, and celebrating their small steps of progress.
Hope this helps. Keep on alsking questions!