Everything family-wise is still the same: Sasha is Hawk and Moth's mother, and Tigerstar is their father, Tadpole dies and traumatizes Hawk, they go to the Clans and become apprentices. A while through their training they learn just how terrible their father was, and both kits try to distance themselves from the tales of Tigerstar. Hawkpaw and Mothpaw earn their warrior names of Hawkfrost and Mothwing, but Mothwing seems unhappy; Hawk notices one day and asks her and she says that she wants to become a medicine cat instead of a warrior. Mudfur evaluates her and after StarClan do bring a sign of the moth's wing to him, he agrees that she can be a medicine cat. And it is StarClan that brings the moth's wing, not Hawkfrost.
Hawkfrost and Mothwing learn that Tawnypelt and Brambleclaw are their half-siblings, and Hawkfrost takes every chance he can to learn about his siblings. He is still traumatized about Tadpole's death and doesn't want to lose another brother. He is terrified when Brambleclaw disappears, but Mothwing is able to comfort him and calm him down. Finally, when they come back, Hawkfrost is relieved and talks to him and gets to know him. In this AU, Shrewpaw doesn't die (becoming Shrewfur) and will become Squirrelflight's mate. They go to the new territory, but Hawk feels that Bramble is acting off but Bramble won't tell Hawk anything. Graystripe is still captured and Firestar doesn't name a deputy until the times of Sunset like normal.
Tallstar still dies and names Onestar as leader, everything normal happens. Hawk and Bramble begin to train with Tigerstar, even though Hawk is hesitant at first, just as Bramble is. Tiger (using his wonderful manipulation) is able to convince Bramble and (he thinks) Hawk by saying he was misunderstood and that all he wanted was the 'right thing' for ThunderClan. The brothers grow closer, but Hawk starts to realize that what Tiger is saying isn't right and that he really does love RiverClan, and especially Leopardstar as his mother. Yes, he still disagrees with Mistyfoot, but they have an understanding that they both want what's best for RiverClan and have agreed to disagree but still work together. The brothers, aka mainly Bramble, work out that they will kill Firestar and make sure that Bramble can become leader quicker.
They both go to the area, and Hawk is horrified to see that Firestar is trapped in the fox trap and finally confronts Bramble. He demands to know what Bramble is doing and Bramble whirls to him. He says that this is what their father wanted and what their family deserved. Tigerstar's father was leader, but he was a terrible coward, and Pinestar's father Oakstar was a real leader, killing kittypets and being a terror in the forest; Firestar is a kittypet and doesn't deserve to be a warrior, much less a leader. This makes Hawk angry and he lashes out, snapping that he's half-rogue, so he shouldn't be a warrior either, right? Bramble responds that he's still half-clan and the son of a leader, so he's fine. Hawk says that it's wrong and that they shouldn't kill Firestar and Bramble says that if Hawk won't kill Firestar, then Bramble will. The whole battle happens normally, but Hawk kills Bramble at the end with the fox trap spike. Hawk stands over Bramble, completely horrified as he watches the light drain from Bramble's eyes and the blood flow into the lake.
There would be a rustle and Hawk whirls to see Squirrelflight coming out of the bushes and looking horrified at what she can see is Hawkfrost killing her clanmate. Hawk tries to tell her what happened, but all she does is run to Firestar, who has lost a life by now, and take the fox trap away from around his throat and take him back to camp. Hawk flees back to RiverClan where Mistyfoot and Leopardstar demand to know where he went and why he's covered in blood, and Hawk tries to tell them what happened. Leopardstar and Mothwing believe him, but Misty isn't so sure. They bring him back to ThunderClan the next day to talk to Firestar and Firestar says that Hawk is right. Leafpool feels bad because her prophecy from StarClan that she thought meant that Bramble would protect the Clan was really a warning. What StarClan had meant was that the brambles around the camp would trap ThunderClan under his rule. Blood had spilled blood and the lake had run red. Firestar names Brightheart as his deputy, with her having Berrykit as an apprentice.
When Leopardstar dies, Mistystar names Hawkfrost as her deputy because they understand different ways of leadership and two cats who argue and have different opinions lead the Clan better than two cats who agree on everything. Mistystar loses a lot of lives in the Great Battle and then dies after Darktail is defeated. Hawkstar rises to power, naming Stormfur as his deputy. Stormfur and Brook remain in RiverClan, having Pinekit and Larkkit in RiverClan. Hawkstar is still leader when the Broken Code is going on, and Brightstar names Ivypool as her deputy. I'm not sure how that would mess up the plot of the Broken Code but whatever.