I'm new to xcode storyboard. I have a viewcontroller that contain two label of same width, but
If you want label 1 to be twice the height of label 2, then control-drag from label 1 to label 2 and select Equal Heights from the pop-up menu. Then find this constraint in the Document Outline and edit it in the Attributes Inspector on the right. Change the multiplier to
If you pin the orange label to the top of the screen and pin the bottom of label 1 to the top of label 2 and pin the bottom of label 2 to the views below, then these two views will fill in the space and maintain their relative vertical sizes.