100% correct. There is no x2 camera.
There is FOUR back cameras(and 1 front), but no x2.
According to camera api numbers
0 - primary
1 - front
2 - depth mono
3 - macro
4 - wide
Yes, you also can use depth camera for some needs.
Every camera is tested and requires different approach.
Depth camera cant be used with gl preview - pixel format is incompatible
Wide cant be used in HDR MODE - grabled picture