How can I prepare aqueous solution using moisture sensitive organosilicon such as tetraethyl orthosilicate, tetrapropyl orthosilicate, etc.? I am afraid that it might hydrolyze before I introduce it into the main reaction.
It sure will - unless you're awfully quick about it. That's the nature of the beast. Are you sure you need to dissolve it in water, or would a water-miscible solvent do as well?
As James points out some degree of hydrolysis is unavoidable. Numerous factors such as pH, temperature, and ratio of water to TEOS to name couple can impact the degree of hydrolysis that you will experience. A good way to quickly become more aware of what can happen in these system I recommend you look at review articles or text books on sol-gel chemistry.
Often times rather than fighting hydrolysis one tends to seek a means to obtain a consistent and reproducibly level of hydrolysis.