It's option 2, it's basically the same concept for flanking a character whose size is greater than yours (more character can flank him).
Here it's the same, because the ogre is taller than the two fighters, when he tries to overrun them, he will have to beat the combined score of the two fighters.
It's to actually encourage teamwork for taking on large or monstrous size creatures.
Opponent Blocks? If your opponent blocks you, make a Strength check opposed by the defender’s Dexterity or Strength check (whichever ability score has the higher modifier). A combatant gets a +4 bonus on the check for every size category he is larger than Medium or a –4 penalty for every size category he is smaller than Medium. The defender gets a +4 bonus on his check if he has more than two legs or is otherwise more stable than a normal humanoid. If you win, you knock the defender prone. If you lose, the defender may immediately react and make a Strength check opposed by your Dexterity or Strength check (including the size modifiers noted above, but no other modifiers) to try to knock you prone.
I checked if something was actully specified for a multi-block, but there is none, it's up to the GM, so you have to choose if yout want to combine the dice score of the two fighters or if you want to make them roll in order.
I'm actually more prone to make a combined throw for the two fighters if the total space they have is less than the ogre: for exemple, your fighters are each 2feet large (it's an exemple) and your ogre 5feet, then you combine the dice score. But if they are larger than the ogre (like 2.8' each) then you make the ogre choose which character to overrun.
you use the same method as the flanking rule to decide:
When in doubt about whether two friendly characters flank an opponent in the middle, trace an imaginary line between the two friendly characters’ centers. If the line passes through opposite borders of the opponent’s space (including corners of those borders), then the opponent is flanked.
But here you actually check if the fighters both fit in front of the ogre. If not you choose.