How do you deal with fundamentalist inlaws?

[TaraJo]

So, in one week, my boyfriend and I are going to the Ren Faire. Yay!

One scary tid-bit about it, though: his mom is taking care of the tickets. I'm sure his mom is a nice enough person over all, but she's also a Mormon fundamentalist and that scares the shit out of me. D:

I think they suspect that he's into women, and they know I'm trans; I don't know if that will make the more or less accepting of Lee and I being together (because, if they're convinced I'm a man no matter what I do or say, then they can look at our relationship as being straight). He tried being straight and settling for dating a male crossdresser before me and I'm not sure how that will play into things; his ex was a monster (to put it lightly) but once is sisters got to see me a little, they told the rest of the family that I'm nice enough; and much better than his ex. I don't think they have a clue that he's trans and it's going to be really tricky for me to switch to female pronouns and use his 'before' name around them, but I think I can do it; I've made the swich before.

Any advice or suggestions or ideas on how to handle things?