NIS for 3 pc's- Can I use it overseas for third pc.....?

Hi,

I bought NIS for 3 pc's last month. I installed it on 2 PC's. I have a question regarding the 3rd one. Can my parents use the third key- they are overseas. Will they need the CD (which I got in the pack) for installing NIS in their PC? Please guide me. 

 

 

Thanks