My two boys are both on minecraft (one as guest & one on Xbox live account) they are both connected to their friend. Only one of the headsets is working. Is there any way that both headset could work so they count both listen & talk to their friend?
To be able to chat in a party, you need to be signed in with an Xbox Live account. On Xbox One, you need to have a Gold subscription to chat in a party. On the Xbox 360, you can only chat one-to-one without a Gold subscription.
In your case, only one account is signed in, therefore only one account is allowed to chat in the party. To be able for both of your boys to chat, the second child would need to sign in with an account that holds a valid Gold subscription.
I would recommend you set up a family using a parent account that holds the Gold subscription. That way you can easily share it with both your children without any additional fee and, on top, you would be able to play around with parental controls.
The Xbox Kinect has a mic which can be used in chat.
As for the listening part, they'll have to not use a headset and just use speakers on the TV. Alternatively, you can buy audio jack splitters (that work the same way as power splitters) that can send the same sounds to two (wired) headsets.