I did a search on J.P. Morgan.
And he was alive from April 17, 1837 – March 31, 1913.
Which means its impossible to evenn serve in WWI.
I looken in his personal like and he had a son named J.P. Morgan Jr. he was alive from September 7, 1867 — March 13, 1943.
So he would have been 75 or 76 to serve in the marines in the miniseries.
I also looked and it said he had 4 children but didnt name them.
So i dont think that one of his decendants is a J.P. Morgan III.