I was playing twilight imperium for the first time and I was wondering:

I invaded my brother's system (a brotherly thing to do), I nuked his puny ship with my war sun and the system only had 2 planet with 1 ground force each,

Can I bombard them both with 1 war sun? How about if I had ground troop, does it change anything? Is it

a) I can bombard all planet in the system with one war sun.

b) I must split my fleet of war sun/dreadnought among the planet I want to vitrify.

c) I can bombard all planet I invade plus one planet I don't plan to invade?

say I send two war sun in a 3 planet system, do I roll 6 dice three times once for each planet ? Even without ground forces?

oh and last but not least, can I say : bombard then if I'm unhappy drop the biological weaponry or can I only chose before an invasion which way to go about invading a planet?

Esurnir said:

(b). You can bombard one planet per ship in a turn (and need to follow the rules for bombardment).

The biological weapon card specifically says you decide before bombardment whether you're using it or not.