49:7 If one recites the bracha over wine during the course of a meal with others, he should say “savrei rabbosai” (“Listen up, gentlemen!”) so that they will stop eating and pay attention to the bracha. (Mishnah Brurah 174:45-46 makes it clear that this is only when others wish to be included in his bracha for their own wine.)
49:8 If they were drinking one type of wine, either during a meal or not, and another wine was brought, they do not recite the bracha of hagafen again because they’re still involved in wine-drinking. They do, however recite the bracha of hatov v’hameitiv, that God is good and does good things. They would also recite hatov v’hameitiv on a third type of wine, etc. In the Jerusalem Talmud (Brachos 6:8), R. Yehuda HaNasi would recite hatov v’hameitiv over every barrel that was opened, no matter how numerous.