Does brambleclaw hate squirrelflight

YES. It may be creepy but it's true! You see, Brambleclaw and Squirrelflight are cousins! Well Technically they are half-cousins but you can call it whatever you want!

Tigerstar and Sandstorm are cousins! Wanna know how? Redtail, Sandstorm's father, is the brother of Leopardfoot, Tigerstar's mother! So that making Sandstorm and Tigerstar related and their children: Leafpool, Squirrelflight, Mothwing, Hawkfrost, Tawnypelt and Brambleclaw, are kin.