That is one more reason why this facility of selecting "consider for auto upgrade" was launched. This applies mainly to solo travelers, and depending on the route and classes booked, may apply for 2 or more ppl on a single ticket too. However, you're quite safe to select the option as long as all pax are on the same ticket and not on different ones - upgrade (if it does happen) is based on avble seats and number of pax on a ticket.