Grooming Miniature Schnauzers

My Mom has a pair of mini-schnauzers. They've been groomed almost exclusively by a professional for their whole lives. However, because it costs so much each time they go in, they aren't being groomed often and Mom's having a difficult time maintaining them in between. I've been trying to help her figure out ways to keep them groomed between groomings, but I've never had such a high maintenance dog myself, so my experience is pretty limited.

Does anyone here have experience with grooming this breed or other really wiry tangly dogs? They don't get brushed nearly enough, partly because their fur is just so difficult to get a brush through. She had tried using a leave-in detangling solution with them, but found that what she thought was a good-quality, natural product was causing her allergy problems (everyone in our family is chemical-sensitive and highly allergic to perfumes). I'm hoping to find a product that's unscented and has only simple, fairly natural ingredients. Anything that's "natural" with essential oils tends to cause problems too.

I'd also appreciate tips on the best tools to use for their coat-type and any other suggestions.