Here's a couple good places to start:
http://www.parktool.com/blog/repair-help
http://sheldonbrown.com/articles.html

Look through the Park Tool pages. They cover every adjustment and overhaul operation you'll encounter on those bikes. If it's too much, try to find a bike co-op near you (it would help to know where you are) and learn the basics.

Now, please don't take this the wrong way: those bikes really aren't worth it. Even if you spend a bunch of time and money on them, they will still be very low quality "department store" bikes. Unless you have some sort of emotional attachment to these particular bikes, I would recommend finding better quality bikes to work on. It'll be easier to find parts, easier to learn adjustments, and generally less frustrating to learn on a "good" bike than what you have there.