Hello everyone - I've been lurking on this site for a very, very long time now, and I'm sort of struggling with an issue that I figured I would post about, if anything just to vent. The community here seems wonderful, and I'm trying to get over my shyness in regards to posting things. Bare with me, and sorry if this is scattered/badly written, I'm not used to posting on forums/opening up to strangers

Next month I'm going to be visiting my partner and their family out of state for a little over a week for Christmas. This is the first time I am meeting them, and meeting any of my significant other's parents, at that! However, none of them, with the exception of their mother, knows I'm transgender. They think I am a cis male. While that is absolutely great now, I am incredibly stressed and worried about passing in person, and worried about any teasing/questioning that may come from it. They are as far as I understand a very conservative family, which makes me much more nervous. Among that, dreading the likely situation that I may have to 'come out' to them, as much as I really, REALLY do not want to.
I'm really torn on what to do. Do I come out to them right off the bat to avoid a very awkward situation later? Or just ride it out and pray they don't notice or say anything?
People say I pass very well in photos, but I have absolutely zero confidence about my ability to in person, mostly since I've never been 'sir'ed or referred to as male once outside of the internet. Being short, having more 'feminine' behaviours, and having a higher voice really doesn't help, either. I know my partner will stick up for me... I'm just absolutely terrified about this whole ordeal.
Has anyone else been in a similar situation to this that has any advice they can offer?

Thank you all very much in advance!!