@AsifSayyad I am not 100% sure what your first question is referring to...you have a Sandbox Canvas instance that is not your normal Canvas instance? I have never seen that before, most people have (or I thought most people have) a Canvas, Canvas Test, and Canvas Beta which all are like school.instructure.com, school.test.instructure.com, and school.beta.instructure.com respectively.
All that said, Catalog only "sits" on top of one instance and the instance it is tied to is the only one that courses can be linked from. This does also mean instances with trust relationships between them can also not be tied. For example, my institution currently runs 2 instances of Canvas each with their own Catalog. We have a trust relationship setup so users can potentially see across the instances and it is not obvious to them that they have courses in 2 different Canvas systems. Even with this, courses from one instance can only be attached to the Catalog that sits on top of it and not the other Catalog we have.
Since the answer is "no", I think this negates your others questions.
Hope this helps!
-Nick