They did the farewell tawaaf and travelled on the 11th, and delegated someone to stone the Jamaraat on their behalf on the 12th

If the situation is as described, their Hajj is valid but
it is lacking to the extent that they missed out by departing before
staying overnight in Mina on the night before the 12^th, stoning
the three Jamaraat after the sun passed the meridian on that day and
bidding farewell after that. Undoubtedly they sinned by doing what they
did, which goes against the words of Allah (interpretation of the
meaning): “And perform properly (i.e. all the ceremonies according to
the ways of Prophet Muhammad صلى الله عليه
وسلم), the Hajj and ‘Umrah (i.e. the pilgrimage to Makkah) for
Allaah” [al-Baqarah 2:196] and the words of the Prophet (blessings and
peace of Allah be upon him): “Learn from me your rituals (of Hajj).” They
have to ask Allah for forgiveness and repent to Him from that. According
to the correct scholarly opinion, each one of them has to offer a
sacrifice of an animal that is acceptable as an udhiyah for not staying
overnight, another animal for not stoning the Jamaraat, and a third for
not doing tawaaf al-wadaa’, because they come under the ruling of one who
did not stone the jamaraat, because they departed before doing so; and
they come under the ruling of one who did not do the farewell tawaaf,
because they did their farewell tawaaf before completing their rituals. 

And Allah is the source of strength; may Allah send blessings
and peace upon our Prophet Muhammad and his family and Companions. End
quote. 

Standing Committee for Academic Research and Issuing Fatwas. 

Shaykh ‘Abd al-‘Azeez ibn ‘Abd-Allaah ibn Baaz, Shaykh ‘Abd al-Razzaaq ‘Afeefi, Shaykh ‘Abd-Allaah ibn Ghadyaan