I am interested in any source that confirms that the Grants descended from Milo fitz David fitz Gerald of Wales.
You are talking about events around 1200, so "confirmation" is difficult, in as much as a letter signed William Grant saying that Milo was his grandfather (or whatever) does not exist .
However you can work with "the balance of probability" and on going through all the sources I reach the conclusion that the Grants are descended from Milo. You have presumably read my web site
However the purpose of this thread is about trying to untangle the Grants who came from Iverk and who are both scattered and still in Kilkenny/Waterford. For example in your own case you need to look at the period 1650 to 1850 - whatever happened in 1200 is not going to help
I would suggest that you start a new thread of your own to discus the origins of the Grants at and before 1200 if you want to go into that. Otherwise the purpose of this thread will get watered down
My own view is that at the moment the only way to untangle the Grants today is by DNA, have you had a DNA test done by a male Grant from your line?