Naruto Questions about the Huugan clan and other related stuff(spoilers)

In episode 61, where Neji and Naruto have a discussion about the past in the midst of the battle.
Im not sure if I get this, the Huugan clan had twins. So the elder son became the head master. Hizashi, became a family branch member. The branch members are cursed with the seal in order to proctect and not harm the Huugan family members. Now, when the lightening country got involve. This is where I got confused. Why would they want to kidnap Hinata? Byakugan secrets? Any ideas what the secrets are? I first thought that they wanted to know how to master the cursed seal technique, but still.. why would they want Hisashi's corpse?
Also, is there a reason given later in the story of why Huugan did not participate in the celebration of the alliance of Konoha and the country of lightning? I don’t see the importance of this being said in this episode, only if there is a hidden reason.

 

Do you remember what Kakashi said about Hunter-nins? They dispose of the mising-nin's body entirely with a flock of crows because within a ninja's body, there aer secrets of the ninjustu. They wanted Hinata so they could find out the secrets of the Byukugan.

The Hyuuga clan probably didn't participate because it was the day the family split into three, it was Hinata's 3rd birthday, and Neji recieved the seal on his forhead. I'm assuming they were a little to preoccupied to attend the celebration that day...but this is only my assumption. Personally, I'm not too satisfied with the explanation, but it's all I've got.