Ok, this is very interesting. Is the problem here that your mom suddenly turns her back on all her atheistic beliefs, or is the fact that she's trying to convert you as well that's the problem?
The first problem is that yes, she did
suddenly do so. I guess that's the whole point of having a sudden spout of inspiration, but it's rather jarring that it would happen over night. I'm not sure how sincere it really is in that case... the second is that now the kids praise God, go to church, etc. I guess it'd be overstepping my role as "the big brother" to say that's wrong and harmful, but they're very impressionable little people. I guess there's no gentle way to approach religion, but telling them something is an undeniable truth before they even know how to tell when someone is lying is... I'm not satisfied, I guess.
You could also try mentioning it in passing to the people in your bible studies group or something. Don't rant like you did here, but just a remark in passing about how you're not sure about all this and are feeling pressured. With some luck, someone with a bit of standing in the community will have the sense to know that a forced conversion isn't wort one hundredth of a genuine one and could try to tell your mother.
Not really going to be pretending anything. It's kind of an affront to religion as a whole, and all it stands for, to pretend to follow something just to influence people. That's the reason a lot of people hate mass organized religion; they believe that some people were using it as a tool of war, which is only so many steps away from "using it as a tool to make people happy". That includes counter-espionage, and I really don't think I could try to persuade people who are perfectly happy with their umm... set of beliefs, I guess, unless they asked. I don't think they go to church to become convinced and to debate, they come to hear what they want to hear.
Also, be careful of what Bible translation you're reading. There are two ends of the spectrum; those that try to translate word for word the original Hebrew / Greek (ESV is pretty much the extreme end), and those that try to translate the meaning of the original (The Message being the extreme of this end). That can actually get you into trouble in some discussions. NIV is common and pretty much right in the middle of the spectrum.
The shiny, glittery bible I received is the NIV. Just noticed that my mom wrote a quote in the inside cover... "This book will keep you from sin or sin will keep you from this book." Not sure where she got that from, but eh. I'm guessing by her ~200$ expenses on a necklace and this book (and it's inscription) that she's convinced that I'll convert... Also, the tithing thing and whatnot seems to be suggested by her church. It's this thing called "the wave", where they have a lot of expensive stereo equipment, sell their worship sessions on dvds, and have celebrities visit. They say all proceeds go back in to the church, or to charity, but I have no way of contradicting that statement.