I read this book and its sequel a while ago. The cover of the first book features an old inventor with keys, if my memory is correct.
The book is set in the near future; somewhere between the 2030s and 2060s--maybe in the late 2040s.
There is a sister and brother who are both quite smart, and they are accepted into an elite academy. The head of the academy is an old inventor, and the siblings happen to be his grandchildren. This academy is extremely advanced; it features avatars, or cybernetic, fully constructed animals that people can connect to.
They can move the animals, and see and feel from their perspective. There is a class in the academy that uses some kind of advanced tech to construct extremely realistic images of the past, and it is based on some kind of time travel.
There is also a girl that is jealous of the siblings.
There are small white spheres containing data that are used for various purposes.
However, there is a real time travel device in the academy, and of course, there are people trying to use the time travel machine for twisted, malicious intentions.
The time travel machine is operated by keys that the teachers possess.
The book came with a trailer. I also think the book was quite popular.
Could someone tell me what this book/book series is?