Nope, they decide who needs to get paid, and then the pool goes to work mining a block that will pay those people. You can't change who gets paid after the block is generated. That would defeat the security of the system.
As for send multiple: any transaction can take in any number of coins, and then has to output the same number of coins. It can come from any number of addresses, and go to any number of addresses. It pulls whatever coins are available in your wallet, and pays out to the list of addresses you want including your "change" which goes to a new address in your wallet. (Normally that's 2 addresses: the person you pay, plus yourself for the change; but it can just as easily be 3 or more.) Any imbalance is paid as a transaction fee to the miner.
That's a little different from the generated coins, since those don't have a "From" address. It's just 50 coins that come from nowhere and pay out to wherever you want (often all one address, but Eligius just splits it out to everyone they're paying).