Constraints for buttons between all device sizes xcode 7

I have three buttons laid out like this in Xcode: http://ift.tt/1DquD8w

As you can see, I have errors for my constraints within my storyboard. I used constraints from a picture that someone from here on stack overflow drew up for me:

http://ift.tt/1Ul0Xyc

I've tried many other constraints but I can't seem to figure out what constraints to use.

How can I fix this so it looks like it does in the storyboard across all iPhones and iPads? Landscape mode will not be a part of this application.

via Chebli Mohamed