To get the buttons to follow the screen you need to move them to a new layer above the main one. This can help separate HUD elements from the rest of the game.
Then you edit the properties of the layer so that the Parallax details all equal 0. The parallax details control how fast the layer scrolls when the camera moves and is often used to create more interesting backgrounds where distant mountains move slower then closer tress, as in real life. With the value at zero, anything on this layer will not move allowing it to remain on the screen at all times!
Another hint, try controlling the location of the HUD elements with the Anchor behaviour. This way the HUD stays on the same place across multiple screen sizes.