Ace is on the execution platform. Kneeling, and chained with Seastone chains and handcuffs to block his devil fruit abilities. Sengoku, the Fleet Admiral, is standing right next to Ace. Garp was also right next to Ace on the other side.

But then after Sengoku revealed Ace's secret to the world of Ace being Gol. D Roger's Son, the Whitebeard Pirates' 43 subordinate pirate crews from the New World appeared before the Marineford Bay. The Whitebeard Pirates themselves appeared in the center of the bay, having coated their ships and infiltrated the bay undetected.

All of them were ready to save Ace. And Luffy was making his way their as well with the escaped prisoners from Impel Down.

The Seven Warlords, are there as well but their isn't really Seven of them since Crocodile isn't a Warlord anymore and Jinbei refused to help the Marines during the war since he's friends with Whitebeard.

Whitebeard walked to the front of the Moby Dick, The Whitebeard Pirates main ship and looked at Sengoku. Marco the Phoenix, the 1st Division Commander and Main Doctor, is right next to Whitebeard.