How do I fix the cracks in my brick foundation?
If the cracks aren't new, then there's really nothing to 'stabilize' as that's already happened over the past 100 years. 

If they are new, then you have bigger problems and need a structural engineer out there to figure out why your footers are sinking. 

Assuming they are old cracks, if you don't have water problems, you don't really need to do anything with them. But if you do want to seal them, and you're going to cover them (so not overly worried about aesthetics) then a hydraulic cement product is what you are looking for such as