I'm a little unclear about what you're asking. Usually, a fact family starts out as being two different numbers that equal a third number in some way. For example, the fact family: 2, 3, and 5. 2+3=5, 5-3=2, etc.
Below, I'm including a link to a question asked about fact families by another member. One of our JustAsk Experts answered it, and gave a helpful definition. It may help to clear things up!