iTunes question
 

I am giving each of my two boys iPods along with matching iTunes gift cards.

They both listen to the same music.

Can each one just piggyback on the other as far as purchased songs or do they each have to buy the songs separately for their own iPod?

You share with up to four iPods from one computer.

I is easiest if you just use one account for the whole family, that way you can share everything between up to 5 computers and (I believe) an unlimited amount of ipods. I have one account on 3 or 4 computers, 3 iphones, an apple TV, and lots of ipods.

Exactly. Each iPod is "tied" to an account once synced. If one were to take an iPod to another account, it would erase the existing music and sync the music from the other account. And iPod can not be synced to two accounts at the same time.