What is entailed for one who stoned the Jamarat before Fajr on the second day of Tashreeq, and what is the expiation for that, and for whoever followed him in the stoning?

The majority opinion is that throwing the pebbles (rami al-jamarat) on the Days of Tashreeq begins after Zawwal (zenith) and ends at sunset. The permissible time extends until the dawn of the following day. However, some scholars permit throwing the pebbles before Zawwal. Your throwing on the first day of Tashreeq is valid, following the opinion of those who permit it. As for your throwing on the second day before dawn, it is not recognized by the majority, and you owe a dam (sacrificial offering) for neglecting the throwing of this day. Another dam is due for the Farewell Tawaf, which occurred before the completion of the rituals. The pilgrims who followed you are subject to the same obligations as you, if they performed the same actions as you.