FDR's family has some potential as well.
James served with some small distinction in the second world war, and had his own political career (10 years in the house, attempts to become governor or mayor of LA). Probably one of the more likely candidates of FDR;s children.
Elliot also served in the war, but is unlikely as a candidate, as he never seemed to have the same interest in politics as his relatives.
FDR Jr. served in the war as well, but never seems to have completed his move into politics. IMO, if you can make him Attorney-General of New York in 1954, he has some of the best prospects from among his siblings. He could quite possibly use it as a springboard to the governorship (this time having greater experience in his own right), and from there to the presidency, or intead do as Javits did and enter the senate.
John probably isnt going to go anywhere unless Eisenhower and the republicans activly push him as a candidate for something.
In short, FDR jr and James were in a position to break into the upper echelons of the political heirarchy, and some different elections (Attorney general of new york and mayor of LA respectivly seem the best options) could be enough to start one on a path to the top.
Of TR;s children, I think Quentin is being overlooked. He was often regarded as being very similar to his father, and if he survives and maybe makes a name for himself he could wind up being a force to be reckoned with.