Hey Kris,
I'm gonna give you a slightly different take, just based on how I would look at it if it were me (and of course it's not, so please feel free to disregard...) So, to me, it sounds like you're considering your Mom's request as a long term thing, when it may actually be more short term. As you mention, the physical changes are going to be apparent to your younger siblings in the not too distant future. It doesn't sound like your Mom is against your transitioning or your seeing your siblings, so to me, it sounds like what your Mom may be asking you for is not that you not be yourself, but that you give her a little time. It sounds like your younger siblings are old enough that at some point they are going to ask her about your appearance changing so your Mom is probably going to be having a talk with them and maybe she just needs some time to figure out how she wants to answer, or maybe she just needs a little time to get used to things herself before she can focus on how to answer? (If this sounds like it might be the case, you could just bring it up point blank: "So, Mom, you know I've been respecting your wishes about not wearing make up around the kids, and the I wouldn't want to confuse them, but some of my other changes are becoming more apparent and have you thought about what you might want to tell them/do you want me to be there to answer questions/need me to point you toward resources, etc?") Once your siblings understand what's going on, the make up might not be an issue. Even if you think this is not the case and/or you don't want to talk to you Mom about it, I think I'd still take a wait and see approach, because you can always re-evaluate and go against your Mom's wishes at a later time, but once you decide to disregard her request, that ship has sailed. Of course, I'm of a very cautious and risk-adverse nature or I wouldn't be the Ghost, and this type of approach may not be right for you, but I thought I'd put it out there just in case. I'm wishing you the best on it.