Napa Valley’s smallest winegrowers may soon be able to host tastings at their vineyards — which they say is a vital lifeline for keeping the region’s family farms viable, and a boon for those who don’t want to see Napa’s landscape overtaken by larger corporate interests. It’s a battle that one group of farmers has been fighting for more than three years. The county’s Board of Supervisors decided last week to explore the issue, and they plan to...