Yes, Firestar is in love with Sandstorm.
Scourge had feelings for Sandstorm, but it was more of a one-sided crush from Scourge's perspective. Sandstorm's heart belonged to Firestar.
Firestar
Sandstorm's first apprentice was Sorreltail.
Yes they are mates. In the darkest hour FIrestar admits to himself that he loves Sandstorm. And she loves him as well! They have two kits in FIrestar's quest named leafkit and squirrelkit and leaf paw, who become leafpool and squirrelflight!
Yes, Firestar has two daughters with Sandstorm, Leafpool and Squirrelflight.
Cinderpelt tells Firestar that Sandstorm likes him but not her because Cinderpelt is perceptive and observant of the dynamics between the cats in ThunderClan. She notices Sandstorm's behavior around Firestar and interprets it as signs of affection. Cinderpelt may also have a close relationship with Firestar and wants to see him happy, even if it means potentially hurting her own feelings. Additionally, Cinderpelt may feel a sense of duty to ensure that Firestar is aware of Sandstorm's feelings towards him.
Yes, Sandstorm almost fell into the gorge but she was saved by Fireheart just in time. Her paw slipped on the edge, and Fireheart grabbed her before she could fall.
No one has sandstorm and Firestar are still alive and they have grand kits
Yes. Firestar started noticing Sandstorm around Rising Storm. An experience that made them connect was when Firestar saved Sandstorm from falling over the gorge. (when Firestar was Fireheart and Sandstorm was Sandpaw). After that, they couldn't stop looking at each other! In The Darkest Hour, they both admit that they love each other and Sandstorm goes to sleep with Firestar in his den when the battle with BloodClan was going on. After that, in the end of Firestar's quest, they have 2 kits named Squirrelkit (later Squirrelflight) and Leafkit (later Leafpool, med cat).
Sandstorm becomes a queen in the seventh book of the "Warriors" series, titled "Firestar's Quest." She becomes the mate of Firestar and the queen of ThunderClan.
Firestar and Sandstorm had their kits sometime between the end of the first series and Firestar's Quest.