BRB's 'Cosmic Storm and Eclipse' is worded as follows:

COSMIC STORM AND ECLIPSE:#Opposing characters within 6 squares possessing the wing symbol modify their speed and attack values by -1. Friendly characters within 6 squares that can use Stealth have lines of fire drawn to them blocked when it's not your turn.

My question is, if I have an entire stealth team and I hide BRB behind them, can an opposing sharpshooter or a colossal figure shoot Beta Ray or his he blocked by the friendly stealthy figures?

They would be able to see him, they would ignore the other character completely for LoF.

The lines of fire drawn to the figure with stealth are blocked...

It does not block Line of Fire to other figures who do not have stealth so Sharpshooters and Giants that can ignore opposing figures when drawing line of fire still ignore those opposing figures.

So yes, Beta Ray Bill can be targeted in your example.

Thanks for the clarification.