When there is terrorism, TTP accepts the fact that it is responsible. Peace talks are being held with them because there are certain conditions that they would like to follow i.e. sharia law / government in their area, end to drone attacks, and freeing of their people from jail
As far as MQM is concerned, they have been sitting in the government for the past 20 or more years, killing people and then making themselves innocent. While Altaf Hussain has more than 200+ murder cases, he is sitting in London. In a nutshell, they are hypocrites. The only thing they want is the separation of Karachi from Pakistan and they feel that is when there would be peace.