There are tutorials on a few websites and on YouTube, I found a couple links for you but you might want to look somewhere else.

Here is one to draw Sweeney:

www.dragoart.com/tuts/1799/1/1/how-to-draw-sweeney-tod...htm

I couldnt find any direct links to tutorials to draw Mrs.Lovett, but like I said there will be lots on YouTube and sites like DeviantArt if you want to go looking for them :) ♥

Well, around the eyes you should do a lot of dark shading... and for Sweeney you need to make his cheek bones high up and round... Mrs. Lovett's nose reminds me of a rabbit's... and the hair's the most fun part next to the eyes(it's also the easiest).