creature swap

Situation
my field has 2 Blackwing monsters and a set icarus, and opponent has 2 monsters
he activates creature swap, do i select the monster i wan give first or tribute for icarus first if i were to chain with my icarus?

Choosing is upon resolution. If your monster book of moon their monster,it will still swap. Also, creature swap doesnt target.

http://yugioh.wikia.com/wiki/Card_Rulings:Creature_Swap

so that means after i chain icarus tributing my monster to destroy his cards, i will swap my last monster to him?

yes

But I think if you chain Icarus and tribute any of your monster to destroy both of your opponent's monsters (provided that there are 2 or less monsters), and if they do not have monsters when creature swap is about to resolve, creature swap CANNOT resolve because your opponent cannot choose any monster to switch over.

I think...

to make things simple
when creature swap resolve, both player will trade with wadeva mob they have,be it token or anything.
if during resolution, either player have no monster. there will not be any swapping