Try this template:

<xsl:template match="BROTHER">
   <xsl:value-of select="count(preceding-sibling::*[name()='BROTHER')" />
</xsl:template>

--
=====================================================
John Cartwright
Associate Scientist
Geospatial Data Services Group
CIRES, National Geophysical Data Center/NOAA
(303) 497-6284
John.C.Cartwright@xxxxxxxx
=====================================================