@MagneticMonkey:
They don't know where the enemy is. Where will he attack? They don't know, they lost the sight of WB.
They don't necessarily NEED to know where the enemy is. The whole point of Ace's public execution is to lure the enemy to THEM. So no matter where he is, they know where he will end up. Losing sight of him prior to the battle wasn't good, sure, but that hardly makes or breaks the deal. It just means that they need to divide their attentions a little to the prison and Marineford; but really Marineford isn't much of an issue until Ace arrives there, so their attentions aren't divided that much. It's just a point in Whitebeard's favor, that's all.
@MagneticMonkey:
They gathered all their fighters in one or 2 points.
They gathered "all the top Marines" to MHQ; it's figurative, not literal. Surely they didn't pull every single scrap of Marines from all over the world. I would bet they still have some capable hands in appropriate places. I was talking to Muddy Gorilla a few weeks back about the World Government and the Nations under it, comparing it to America, and I suggested that the Nations are the "States" to the World Government's "America". America (World Government) has control of the military (Marines), and while it might get involved with escalated issues within any given state (Nation), it's primary duty is the protection of the country (World) as a whole. Each state (Nation) likely has it's own police (Army/Warriors), special task force (Elite Fighters), and investigation unit (Intelligence/Spies), so they likely do not rely on or necessarily need the military's (Marines') involvement whenever they face an issue. Given these examples, you can sort of see how the Marines are not the only force in the world that watches over islands and nations, and that even if they are gathering their top brass, they likely left a few capable people at their strongholds during the course of this war. So, like I said, try not to take it too literally. If you must take it literally though, read on:
@MagneticMonkey:
They barely know what the other Yonkous are doing.
They don't have much of a choice. Sure, this is an opportune time for any pirate seeking glory and fame, but if the World Government ever plans to do anything about Whitebeard then they have to deal with what comes with that. The thing is, if/when they take Whitebeard down, they will still have most of their power behind them after the battle, while the other weaker pirates and Yonkou will have LESS power due to the "Strongest Man in the World" no longer being around. This would mean, to both the WG and the Pirates, that it's only a matter of time until the rest are taken care of and rounded up. Whitebeard is the primary threat; the first of many that will fall in a domino effect. (From their perspective). Once they are done with the major pirates, they can focus more on Dragon. I'm sure that the Marines (or the WG) believe these to be practical and worthy sacrifices for taking down their biggest threat to the World.
@MagneticMonkey:
What about Dragon? That's like inviting him to take down many WGs countries.
Not really. Dragon takes down countries by spurring civil war and the likes. Remember what I said earlier about the other nations? They without a doubt have their own forces and their own power to help protect them, so while this is a good opportunity for Dragon to exploit, it isn't an invitation to do that much. Like I said though, what other choice do they have if they plan to take Whitebeard down? Any difficulties Whitebeard's issue brings can be taken care of afterward when those other gigantic threats are no longer existant. If not now, EVENTUALLY they would have to pull all their strong forces to take Whitebeard down, unless they plan to continue to lose forces to Whitebeard and have nothing change. What better time than when they have one of Whitebeard's top brass in their hands and about to be executed? What better way to ensure victory than to lure him to your base of operations where you have most of your top men at hand?
@MagneticMonkey:
They're counting on the Shishibukais who are pirates in this war. They are counting so much on them that they sent one of them in prison and threaten him and Hancock to strip of their title if they don't help.
They aren't counting on the Shichi. They are using them. That is what they are for. Their sole existence. If you paid a criminal to do some dirty work and gave him immunity, wouldn't you want him to show up to do his job? If he wasn't coming wouldn't you threaten to take away his immunity and throw him in prison where he belongs? Wouldn't you still want to make use of his special abilities if you still could? Wouldn't you throw him in prison if he rebelled against you? Dealing with criminals isn't a great idea, I agree, but this was something established long ago, so I am sure they made it an option that would work in their favor. If not, then that was poor planning on their part years ago and not simply due to the war. They are just forcing the Shichi to do exactly what they were meant to do, giving them the option to do it or lose it. In some cases we already know they are losing it (Jinbei).
@MagneticMonkey:
They held Ace at ID and are confident that they will manage to transport him safely to the MHQ. They are inviting the opponent to take them down while transporting Ace.
Again, not really. They will be transporting Ace (secured) via a MARINE-ACCESS-ONLY pathway from one Gate of Justice to another Gate of Justice. Anyone who attempts to enter that path and rescue Ace will end up at MHQ whether they like it or not, else they will be forced to continue sailing in a big circle forever.