The halachah depends on whether or not the people listening to the beracha have two loaves of bread of their own. If each person at the table has two loaves and they rely on the head of the table only for the recitation of the berachah, then they may all partake of their own bread immediately after hearing the berachah of the mekadesh.
They do not need to wait for him to first take a bite out of his own Challah. If, however, only the head of the table has two loaves and the others rely on him both for the berachah and for fulfilling the obligation of Lechem Mishneh, then they may not eat of the bread before the head of the table. They must wait for him to take a bite of bread, and only then may they partake of the bread.