How do you resolve two Cylon Attack Crises cards?

First player pulls one and then the second player pulls another? Do you setup as much as you can and then activiate all the ships?

There are three different steps to the Crisis attack cards. First, you activate the appropriate ships (raiders, heavy raiders, basestars) just as if a regular crisis was being resolved. Next, you setup new attacking ships per the picture on the card. You can only set up what components you have, so if you already have two basestars on the board (for example), you cannot place a third. Finally, you resolve any special rules on the new attack card.

Important bit - when you resolve a Cylon attack (or any other instruction to place ships on the board) you add the ships to those already on the board, rather than replacing them.

As stated above, if you run out of ships to place, the current player decides where to place the ones you do have.