I agree, a shampoo and condition are the best start.
As for brushing, yes, they can be brushed, but it's best to section it off and do it slowly from the tips of the hair down. Don't use a big bristled hairbrush. Use something with small, little bristles. I'd suggest a teaser brush. This is what I use on mine, when I get PP in, and even if I just need to fluff one out, I use the teaser brush. You will lose a bit of material, but the fact you gain a lot of body, makes up for it.
I use something like this: [link removed ~ many thanks ~ hathorcat]