A tom cat is just any male cat -- it's not a breed. If you don't know what breeds yours are and you have a tabby (meaning she is striped -- see the thread in the "breeding" forum called "what kind of tabby" if you want to see which kind she is) and a black cat with some white markings, the most likely breed is not really a breed at all. They are most likely domestic cats, which are often outcrossed with other breeds so you can't really pinpoint it anymore. But who knows -- can you tell us what their fur is like or post pictures?