What specifically did the mutineers do to the officers after they took over the ship

Twenty-two men were slaughtered, five men were set adrift (including the captain). Augistus was held by the mutineers, as Peters insisted upon keeping him as his clerk aboard ship.

A scene of the most horrible butchery ensued. The bound seamen were dragged to the gangway. Here the cook stood with an axe, striking each victim on the head as he was forced over the side of the vessel by the other mutineers. In this manner twenty-two perished, and Augustus had given himself up for lost, expecting every moment his own turn to come next.

The mate went down into the cabin to see if Captain Barnard was still living- for, it will be remembered, he was left below when the mutineers came up. Presently the two made their appearance, the captain pale as death, but somewhat recovered from the effects of his wound. He spoke to the men in a voice hardly articulate, entreated them not to set him adrift, but to return to their duty, and promising to land them wherever they chose, and to take no steps for bringing them to justice. He might as well have spoken to the winds. Two of the ruffians seized him by the arms and hurled him over the brig's side into the boat, which had been lowered while the mate went below. The four men who were lying on the deck were then untied and ordered to follow, which they did without attempting any resistance- Augustus being still left in his painful position, although he struggled and prayed only for the poor satisfaction of being permitted to bid his father farewell.