Whichever brother wins the Labour leadership, what will he do with the other? I will come to that in a moment, but first there is a more difficult question, which might be called the Maria Problem. Imagine, if you will, the victorious Miliband surrounded by nuns, asking them, "How do you solve a problem like Ed Balls?"!
In his interview with this newspaper today, Balls renews his bid for the post of shadow chancellor by promising, in effect, not to use it as Gordon Brown did, as a base for his ambition to succeed to the leadership. And, "to be fair" to Balls, to use a phrase that Tony Blair over-uses horribly in his memoir, there are important differences between him and Brown. The first is that Balls will have fought a leadership election and lost it, probably quite badly. It is quite possible that Balls will come fifth of the five candidates. The second is that he does not share Brown's psychological flaws: he does not behave so badly in meetings and he is at ease with members of the public. As we discovered last week, he is the only candidate who can accompany a student with an electric guitar on the drums. But there are similarities – indeed, continuities – too, and Balls as shadow chancellor would replicate the tensions between TB and GB even in different psychological forms.
It is a difficult decision, for either brother. Balls is the most intellectually able economist on the Labour side in the House of Commons. His recent speech on the deficit was praised not only by Martin Wolf and Samuel Brittan, two of the heaviest of the Financial Times's weights, but by Boris Johnson, the Conservative mayor of London. True, his argument that Alistair Darling planned to cut the deficit too fast by halving it in four years, unnecessarily complicates the Labour response to George Osborne's Budget, which plans to cut the deficit altogether in five years. But Balls has proved to be the most formidable critic of the coalition's economic policy.
Yet the media story of his appointment as shadow chancellor will be, if David Miliband is leader, the perpetuation of the Blair-Brown divide for another generation, or, if Ed Miliband wins, the war at the heart of the Brown supremacy. That is why I think that neither brother would actually appoint him to the Treasury. David because he has the intellectual confidence to do without him; Ed Miliband because he will be obsessed with appearing to have the confidence to do without him. Whichever brother becomes leader, it may be that he will make Yvette Cooper shadow chancellor and offer her husband the post of shadow home secretary.
This fulfils three large objectives of shadow cabinet-making. One is to have a credible woman in one of the "great offices of state"; another is to have a "tough on crime and immigration" message; the third is to keep Balls away from the Treasury. Inevitably, the third objective is somewhat compromised by the marital connection, but Cooper is a strong personality in her own right. Not to everyone's taste as a television performer, perhaps, but I recall her role in prompting Harriet Harman's reply to Osborne's Budget speech in July, which suggested that she was quick enough to find the weak point in real time. (It was that Sir Alan Budd's independent forecast was for lower growth as a result of the Budget.)
That, in turn, poses the question of a post for Alan Johnson, the present shadow home secretary who is, I am told, running for re-election to the Shadow Cabinet. I do not know about Ed Miliband, and doubt if Johnson would stick around long if he won. But I suspect that David Miliband would want a big role for him, possibly shadowing Nick Clegg but without being called Shadow Deputy Prime Minister, which might put out of joint the nose of Harriet Harman, Labour's deputy leader. (Jack Straw, who is retiring from the Shadow Cabinet, currently rejoices in the formal title of Acting Shadow Deputy Prime Minister, as well as Shadow Lord Chancellor and Shadow Secretary of State for Justice.)
Having solved the problem of Ed Balls, the winning brother then needs to find a slot for his sibling. Here the temptation will be to leave him where he is. If David Miliband wins, he could offer his brother an expanded green portfolio, covering transport as well as energy under the heading of climate change. Or he could give him health, knowing that in opposition it would be safe to have someone who was not a moderniser there, and that Andrew Lansley offers an easy target that even his brother could hit.
The important point about the reshuffle is that it will not take place until the middle of next month, after the Shadow Cabinet elections. The delay means that there will not be such a premium on appointing defeated candidates to high positions in the name of party unity. Indeed, there will be no requirement to appoint Diane Abbott to anything, as she is unlikely to be elected to the Shadow Cabinet. And it is quite possible that Ed Miliband, if unsuccessful in the leadership contest, would poll poorly among Labour MPs.
As for Andy Burnham, he could go to education, where a moderniser really is needed to oppose Michael Gove on something more than "cuts". Last week's decision by Labour MPs to continue the tradition of electing senior spokespeople in opposition was a bad sign of the durability of left-wing conservatism; even worse was the decision to elect a chief whip to serve a full parliament, in effect with a power base separate from the leader. But a strong leader still has enough scope to be able to weld an effective opposition from the disparate talents available.
It is a tribute to the intellectual force that is Ed Balls that the new leader of the Labour Party will have a bigger and more far-reaching problem deciding what to do with the candidate who came fourth or fifth than with the runner-up.
John Rentoul blogs at: www.independent.co.uk/jrentoul