Importing multiple STL files and keeping relative positions

Greetings.

I am opening multiple STL files representing different components of a heart. (left atrium, RA, LV, RV, SVC, IVC, Pulmonary artery, Pulmonary veins, Aorta) in Photoshop

However when I open them using file open I get several open tabs.

Opening one then using the 3D menu to add new objects works, however when I add a new object (I'm not in front of my PC so can't recall the exact menu choice), it opens in the scene but not in the correct relationship to the other segment.  It would be possible to manually align them, however I would no longer fully trust the accuracy.

Is it possible to open multiple files at once while keeping the correct relationship to other 

Thanks

David