When I hear that "no JW never killed another JW in a war.." in a speech , I usually think at WTS claiming Abraam being the first JW ever.
So the Israelites were JWs. Now give a read at I and II King or the Chronicles (II Chro 13:15-17; 28:5-8) books and find out how many JWs were engaged in wars.
And if was fratricide too. The 10 tribes versus the 2 tribes ..JWs versus JWs.