I agree with Faux Pax’s assessment. Prince Charming was referring to Snow and him as “family” since they were about to be married or already were by that stage. Husbands and wives often refer to each other as family (with or without kids), and they are, by marriage and commitment.
"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy