Hairballs

The kitties have been having hairballs all spring and I've been sporadically giving them the malt flavored tube remedy which helps temporarily. Back when I had a cat for the first time and needed advice, a friend said I should avoid the petroleum based remedies because they're nasty to a cats insides. Looking online I found two natural suggestions: brush your cat every day and prunes. The brushing the cats everyday was also supposed to help strengthen the bond between me and the cat. The gentle, skittish, half-feral one in particular loves it. The oldest, feisty one doesn't like being touched anywhere but around his face, so he doesn't get much. The youngest tends to get her claws out for play time after a few strokes and I've usually forced to stop or lose the skin on my knuckles. I think the recommendation of prunes was referring to prune mash. Has anyone tried it? Does anyone have any other suggestions?