How long are "brief statements of research and teaching interests"?
Coming from pure math at a research institution, typical lengths are 1-2 pages for teaching statements and 4-6 pages for research statements.  However, some people go overboard (e.g., including loads of teaching evaluations) or write long research statements (8+ pages) targeted at experts.  I would interpret "brief" to mean: don't do this.  Moreover, if the school is not much of a research school, I would recommend the research statement being closer to 2-3 pages.

Incidentally, I don't think having page lengths written into the job ads is a good thing.  This isn't a high school assignment.  You are free to say how much you want to, in what format you want to.  Some 2-page statements take longer to read than 4-pages ones, depending on how they're written (bullet points, figures, references,  etc).