Of course, not. Even both of you have the same prescription, you still can not wear her contact lenses. Moreover, you and you sister are not completely same. As you know, our eyes are very sensitive and fragile, even a tiny sand enter your eyes, you will feel uncomfortable. So the most important is sanitation. If you wear contact lens, you may bring some bacteria to your eyes, even infected. So I suggest you buy another one quickly.
No, you should not wear your sister's contact lenses although she has put them in the solution for the night. They may contain the bacterium in the surface of the contact lenses. Once you wear, your eyes may get infection easily and may get the pink eyes. You should buy the new one for yourself. You should keep notice of it. It is the personal thing which should be hygiene.
Well, your plan sounds really nice. And I think that would save you a lot of money. However, be ware! That would give rise to some infections to each others eyes. Because once any one of you get sick, the other gets sick before long. And that way is really unhealthy and dirty. Both of you have to take care of each others' health and try to make clean and proper use of your eyes.
Absolutely Not. you can not wear contacts that other people have worn, because it has been infected so many bacteria which will injury your eyes. More importantly, even though it is your own contacts, you need to get it rinsed with the solution regularly to keep them clean.