Hi, all;
I have been tasked with standardising the format of every publication that the charity for which I work puts out. We are an organization of university student volunteers who teach elementary school students about conflict resolution. The typeface we are looking for is easily read, but not too austere. Because our message is that important subjects can be taught through games, we want our standard typeface to be professional and legible, but also somewhat casual and accessible. And, because we have no money, we'd like it to be in the public domain. The primary documents we produce are:
--Letters to schools interesting in participating in the program (read by teachers and principals; 1-4 pages long with images)
--Letters to local businesses asking for donations (read by professionals; 1 page long with no images)
--Promotional materials for prospective volunteers (read by university students; 1 double-sided brochure with images)
--Annual curriculum (read by university students; 50-80 pages with no images but lots of formatting)
--Student handbook (read by elementary students; 50-80 pages with a few images and lots of formatting)
--Business cards (given to just about everyone)
Ideally one family could be used for all of the above, but I understand that that's asking for a lot. Even a few different typeface families that went nicely together and met the above criteria would be extremely helpful.

Thanks in advance,
-L