If you are calling your VITs dynamically you need to include them in the support files for the project otherwise the executable will not work.
However, I did not quite understand your second question. Do you mean whether it is possible for you to call the same Vit multiple times in the same VI? If that is the question then the answer is yes. Please refer to the following link for more information on the difference between VIs, vits, and reentrant VIs.
I hope this helps!
Mehak D.