I don't have an answer for this quite yet, but plan on coming out to them later in the month.
My family has been very friendly to the Gay and Lesbian community, backing marriage equality, supporting their friends, and sticking up for mine as well. However they have certainly shown indifference or opposition to issues related to the Trans community. It is their openly transphobic remarks about people they know that concern me the most. So basically I am hoping that their open-mindedness might extend a little bit.