Yes, Sandstorm is Firestar's mate and their kits are Leafpool and Squirrelflight.
In the "Warriors" series by Erin Hunter, Firestar mates with Sandstorm, who is a former warrior and later becomes a queen. He does not mate with any other she-cat while she is a queen.
Yes, he died in The Last Hope.
You don't ever really find out, until the eggs hatch, or not hatch in the spring. Because, even if she has not mated, she will still lay eggs.
Polar bears have mated with Grizzly bears. http://www.msnbc.msn.com/id/12738644/GT1/8199/
Firestar is not yet dead, and we do not know who will kill him.
Perhaps in dreams, but otherwise, no. I don't think so
No male duck will ever turn into a female duck.
When Firestar was the kittypet Rusty, ThunderClan was closest to him. He was for their prophecy, and they accepted him into their clan. He didn't ever want to switch his clan, so he couldn't and can't be the leader of them.
No, Firestar does not see Princess in the new territory. Princess only appears in the original "Warriors" series and does not make an appearance in the later books that focus on Firestar and his leadership of ThunderClan in their new territory.
Of course. None of the cats will live forever. He will probably die in the series Omen of the Stars.
Well, that's a matter of opinion, so it's up to you to decide.
No, they live forever. I'm kidding. Yes, of course they die.
Louise Rennison was crowned the first ever Queen of Teen in 2008