Tricky situation. Have you already signed a contract? I only ask because, disregarding all the trans stuff at the moment, there's no guarantee you'll even like the guys you're with, which would instantly make things even more difficult. Is there no way you can meet them a little earlier, before you move in? If you have the opportunity to meet them on "neutral ground," as it were, you might be able to better gauge the situation. The tricky part is that, unless you pass REALLY well, you being pre-T is likely going to raise a lot of questions in their minds. It's unlikely they'll say anything but, unfortunately, they probably will be wondering "what the deal is". Being trans probably won't be the first thing that crosses their minds, though. The unfortunate truth of the matter is that depending on how well you pass it might well be that they simply read you as female (which, of course, is not ideal)
If they do read you as female you're going to either need to be assertive and correct them, or be prepared to disclose your status. I know it isn't an ideal situation but unfortunately that might be the safest way to go forward.
If it's worrying you perhaps you might consider shooting them a quick email in advance. If you're not happy to tell them that you're trans you could maybe just say that you've got some kind of hormone imbalance that causes you to look a little younger than you are, and that you're pretty sensitive about it. Just say maybe that you were getting anxious about it and just wanted to flag it up in advance so they're not caught by surprise and to put your mind at ease.
It really is a difficult situation and I completely feel for you, it's not easy and I don't think you should have to disclose that you're trans if you don't want to, but it's really just a matter of what makes you comfortable. In the interest of safety it would be good to prepare an excuse or defence in case they do start asking awkward questions (like the previously mentioned hormone issue) or just let them know in advance so that at least both parties can be prepared.
Having said that, there might be no issues whatsoever and they might even be totally cool with absolutely everything and ask no questions, which would be lovely.
Sadly, whichever way you look at it, going into a house with strangers is always going to be a risk, even for those without the added issues of being trans. It's good that you're taking steps to conquer your fears but try not to put yourself in unnecessary difficulty. The biggest piece of advice I can really give you is try not to worry. I would, personally, be very tempted to just write them beforehand, either with an "excuse" or just saying "hey, just to let you know, I'm transgender. So yeah. Just wanted to make things easier for the both of us."