To answer one of your questions, both parties worked side by side with the other during both revolutions. Each party, of course, had their own leader. The Mensheviks' was Leon Trotsky, and of course, the Bolsheviks' was the iconic Vladimir Ilich Ulyanov, AKA Vladimir Lenin. While the Bolsheviks were the more militant group, each party played huge roles in the overthrow of the Russian Tsars. Quite simply put, the Bolsheviks, along with a few Mensheviks, marched into the Tsar's Palace, and murdered Tsar Nicholas and his family. If you want a source, let me know and I will try to get one as soon as i can, I wrote this on mobile.