Automate PNG Object - Straightening for Bulk Processing

Consider these two steps:

Assuming you have several tilted image files, each on a transparent background. (Fig 1)

File > Automate > Crop & Straighten Photos. -- actually just one (Fig 2)

Image > Canvas Size --  and enter a finished size: not relative (Fig 3)

Repeat for each image,  perhaps as an Action

Can you post some screenshot with image(s) and desired output result? Do your images have same dimensions and aspect ratio (width versus height)? I do not understand (probably and many others) what exactly is your task, with screenshots you will increase chance to solve the problem. Photoshop action can manage to expand canvas to some specific dimensions so you will get uniform dimensions with transparent areas around but only if images to process shares same dimensions/aspect ratios.

Are the image taken so the background can be removed with an automated process like removing a chromekeyed background. The Image Processor Can Process RAW files and include an action in the image processing. It does not save PNG you Action would need to do that.  There is a better Image Processor Pro that can be downloaded  it can save PNG files. However, your action would still need to be Included in the Process. To remove the background, straighten the subject and add any required transparent borders.

I do not thought know exactly what you means where you write "uniformly sized by height and uniform transparent background size".  You  gave no information about Image size aspect ratios and orientations.

Photoshop scripting can get the canvas size and aspect aspect and other information about the the document. However, I know no way to determine if the  camera was level when the image was captured or what perspective an image may contain.  There may be no image content that would indicate if an image is straight or not. A Baseball flying through the sky. What was the camera for the shot it was not  level. All you see in the image is a baseball in the blue sky..