Two headsets

Also, if they are sharing one account, only the player with controller 1 will be able to use a mic/headset.

Hmm...Did you try go to settings and make the voice better or do you mean some thing else?

I think it partly depends on support from the game. I was paying Halo Reach yesterday and saw that someone was playing 4 player splitscreen yet their account and one of their guests were chatting and had mics in. What headsets specifically do you own and
how are they connected? When you say you can only hear the sound please be more specific. Are you refering to the game audio but cannot hear chat? Can you hear chat from other people on Xbox Live in either headset? You will not be able to hear each other chatting
unfortunately unless the headsets support it such as an Astro Mixamp or Razer Chariacas (which require local daisy chaining).

Hi there.What exactly is going on when you try to play them both? Generally they won't be able to hear each other over LIVE when they're on the same console, but others in the Party should be able to hear them.

The game won't send your voices through the headset because if you are sharing a TV screen you are in the same room.

Other players will be able to hear you though.