can we charge a customer for buying and using their brand fonts?

This is not really a technical question, but a business question.

If a client requires use of a font that you do not currently have a license for (with very rare exceptions, you don't purchase fonts but rather purchase licenses to use fonts), purchasing such a font license is a legitimate business expense. Whether you choose to charge them for the cost of licensing the font really depends on (1) whether you think that billing the client for a relatively low cost item is prudent, (2) whether you expect a long term relationship with the client in which case it might be prudent to simply “eat the cost” of licensing their corporate logo font, and/or (3) whether the font in question is fairly generic and might be useful for use in other clients' work (although preferably not as part of a logo). For either (2) or (3) you would consider the cost of the font license as a longer term investment.

          - Dov