My understanding is the watch crew on the Californian saw rockets but they thought they were 'company signals' not party rockets. The various sources I've read on it never really explain that but I have to assume that ships of the same company would signal each other with rocket signals.

I know there has been a discussion of various things Captain Smith may have done to include getting underway again. I don't know answer as to whether that would have impacted the rate of flood or not. I think the probable answer is that by time the Captain realized that the Californian was not going to respond to his various signal attempts Titanic was no longer navigable. The boilers had dumped most of their steam load, would have taken hours to rebuild and she was listing badly towards the bow. They also had no way of know the extent of the damage to bow, so they had no way of knowing what would happen if they started the engines again.