So what's happening is: Whitestar(Leader of shadowclan) took over riverclan and he made Greyfur and Otterwing kill Bronzeclaw's sister Goldfur,Whitestar asks Bronzeleaf if he will join and Greyfur watches them,but Bronzeleaf knows that Whitestar is evil,and refuses to join,and Bronzeleaf is forced to watch his sister die.Later otterstar (otterwing) askes for an apology because she killed his sister, but bronzeleaf refuses.
Credit to Flamepaw8 and -SkyStar-