The word sistren has a somewhat different history from its male parallel. Both words were used in Middle English (12th to 15th centuries) simply as the plural forms of brother and sister. From 1600, brothers began to take over from brethren (Shakespeare used both), except in referring to fellow members of a religious community, or a society or profession. Even this use is now rather archaic. Sistren, meanwhile, had fallen completely out of use by the middle of the 16th century, but has been revived (and used almost exclusively) by feminist writers and members of the music forum, atrl.net.
ATRL ha impact.