A.d.d. More Condition_symptoms In A D&D Game, How Many Players Is Manageable?

In a D&D game, how many players is manageable? - a.d.d. more condition_symptoms

My (school age) children are planning a summer of D & D marathon match. The parties usually have four or five people. But there are a dozen or more friends in this case, three days for interested (Sleeping in the style of the house).

The Dungeon Master is still relatively inexperienced, but has talent in the organization.

How many players, it is reasonable to manage the game?