match size of multiple layers

Good question, this is one of those things that is there but easily missed. On the PC do a

1. ctrl T to transform your layer
2. click the chain icon(maintain aspect ratio)
3. right click on the width and change that from percent to another unit 

You can also do this quicker by instead doing a ctrl T, then entering for a value in your width followed by the units abbreviation(eg: px), to force this to pixels. I do find it annoying that you have to continuosly keep clicking on the maintain aspect ration, but if you have many of these to do, I suggest recording an action.

That could be done in a script.  However making images layers the same pixel size will not make image have the same scale unless there were all shot with the same focal length  lens and focused at the same distance.  You also wrote all the layer are the same size so I don't understand what your question is in reality.