whereas, on the other hand

My older brother talks a lot.

兄は口数が多いです

My younger brother is quiet, whereas my older brother talks a lot.

弟は静かな一方、兄は口数が多いです

My younger brother is quiet, whereas my older brother talks a lot at gatherings.

弟は静かな一方、兄は集まりでは口数が多いです

My younger brother is quiet, whereas my older brother talks a lot at gatherings even in front of people he has just met.

弟は静かな一方、兄は集まりでは初対面の人の前でも口数が多いです

My younger brother is quiet, whereas my older brother always talks a lot at gatherings even in front of people he has just met.

弟は静かな一方、兄は集まりでは初対面の人の前でもいつも口数が多いです