"to take his yevamah": What is the intent of this? (Why not just "to take her"?) Because it is written (6) "and it shall be the bechor that she shall bear," I might think to exclude (from chalitzah) a woman who can no longer bear, and an old woman, and (the tzarah of) a woman incapable of conception, and a minor who is not yet able to bear; it is, therefore, written (here, twice) "his yevamah," "his yevamah" to include (the above as requiring chalitzah).
"then his yevamah shall go up to the gate (of beth-din) and to the elders": It is a mitzvah for the beth-din to preside in the heights of the city and to be composed of elders."