What you have now is Frank Ralph
Smith Sr., Frank Ralph
Smith Jr., and Frank Ralph
Smith II which is the same as Frank Ralph Smith Jr.
Then when they grow up, they're going to be competing for who is rightfully the III, etc.
You need to have a linear progression. The new baby is Frank Ralph Smith III. But of course, they could name him Frank Ralph Smith the 53rd if they wanted.
It just wouldn't mean anything.
Best wishes, and congratulations to your friend.