One of the features of my subclass is the proficiency in Wisdom(Insight) checks. I want to set up the subclass so that if you already had proficiency in Wisdom(Insight) checks, the proficiency bonus is doubled. I believe that I have to add a modifier, but I do not know how to add what I am describing. 

There is currently no easy way to either grant a proficiency or to grant expertise if the PC that proficiency. You would have to set that up using “optional and trust the player to pick the correct one.

I understand. Thank you for answering both of my subclass questions.

As usual, happy to help.