How to avoid/restrict investing in the same stocks in different pies.
You can’t. You can have the same stock in different pies.
I would suggest the use of Excel.
Put each pie elements in another column and then use the function highlight duplicates, after this you can remove the duplicates form the pie you want.
And the next time you want to add a stock to a pie or create a new pie you can just hit search.
Hope it helps.