The Twins divulging deep things inside,
A part, no doubt of Billionaire 1's pride.
Crucial moments of time or ways to prospects better,
Building necessities, extras to what holds your letters.
What are we?

We are WINDOWS.

-The Twins that divulge deep things inside are the eyes. Often referred to as the 'WINDOWS TO THE SOUL.'

-Billionaire 1 is of course the Top Billionaire, or Bill Gates. [MICROSOFT] WINDOWS, his creation is no doubt a part of his proud accomplishments.

-A WINDOW is a moment in time in which something must take place. It is limited, or crucial. (e.g. "We only have a 30 sec. window to launch")

-A WINDOW OF OPPORTUNITY is a possibility, or prospect of something better.

-Buildings need WINDOWS, but ENVELOPE WINDOWS, aren't necessary, but are added so one can see the inside of a letter at a glance.