Sounds like you have some riding experience, but your friends have not. They should take the MSF beginner course. It establishes a good set of riding habits from the beginning. While it is true that you don't have to take the course, it is to a beginner's benefit to do so, if you learn on you own, you won't be able tell if you are doing something wrong. A good instructor can point out mistakes and show you how to do it correctly. That way a beginner can get started out on the right foot.
Can the 900 be a good beginner's bike? That depends on the individual. Are they strong enough to handle the weight? I'll have to say that learning on a smaller-displacement, milder bike sure involves a lot less stress on a new rider, not having to deal with the weight of, say, a Vulcan 900. But if the person is up to it, the 900 can be a very good bike to learn on. The added benefit to it, is it makes a very nice bike for even an experienced rider. I've been riding for 40 years, and I really like my 900LT.
"Don't sweat the small stuff---it's all small stuff"
'09 650 VStrom