The Basic Numbers
All four players will be seeded in both Rome and Madrid, and will get first round BYEs. Therefore, the points they can earn (in each of the tournaments) are:
R2 loss - 10
R3 loss - 90
QF loss - 180
SF loss - 360
F loss - 600
W - 1000
David Ferrer & Rafael Nadal
First of all, it's important to note that Ferrer's Estoril results won't be relevant to these caculations - he already has an ATP250 tournament win (worth 250 points) that he can't count, so even if he wins Estoril his current points total won't change.
Stripping away the points Ferrer and Nadal are defending in the two clay Masters 1000 tournaments, Ferrer has 6380 points, and Nadal - 4895 points. That's a difference of 1485 points between the two, which Nadal will have to overcome in order to get to #4. Thus, we can start analyzing.
If Ferrer gets at least 515 points in both tournaments combined, he'll stay #4 until the French Open, regardless of Nadal's result. Thus, Ferrer will be #4 if:
- He reaches the final of either of the tournaments
- He makes at least a QF in one tournament and at least a SF in the other
Furthermore, Nadal has to get extremely good results to even have a chance of getting the #4 ranking. If he wins less than 1485 points in both tournaments combined, he'll stay #5. Thus, Nadal has to win one of Madrid/Rome and make the final of the other, and even that might not be enough if Ferrer's results are good enough. If Nadal fails to win Madrid, Ferrer only has to win two matches during the two events to stay #4.
Andy Murray & Roger Federer
Without the points of Madrid and Rome, Andy Murray has 8480 points (he didn't play in Madrid last year, and lost early in Rome), while Federer has 7310 (he won Madrid and reached the Rome SF in 2012). That's a difference of 1170 points in Murray's favor.
If Murray gets at least 830 points in both tournaments combined, he'll guarantee himself the #2 seed for the Roland Garros. Murray will be #2 anyway if:
- He wins either Madrid or Rome
- He reaches the final of one tournament and the SF of the other
Federer, like Nadal, has to make it far if he wants to get to #2. If he wins 1180 points or less, he'll remain #3. Therefore, Federer has to do one of the following to have a chance at #2:
- Make the finals at both tournaments
- Win one tournament and reach at least SF at the other
Of course, all of those scenarios can't all happen together - out of the four players, at most one can win each of the two tournaments. The draw in Madrid might even make some of these options unreachable. But until then, you can at least know what you want your favourite player to do.
Edited on May 9: Federer's loss means that he won't be seeded #2 in France; but at most #3 (can even fall down to #4 if Ferrer does really well in Rome and Federer does not).
Personally, I think the Roland Garros seeding committee should follow the rankings as they are. The concept of protected ranking exists in the ATP for cases just like this one, when a player has been away with an injury for a long period of time. The rule, not accidentally, states that protected ranking will be used only for determining entry lists, not for seeding. There's no good reason to deviate from that rule now, and changing the seeding to fit a specific player (or a specific group of players, in this case) is a dangerous and unfair precedent.