Simple search in Sunni books of Hadeeth leads to the fact that all the three whom you named ran away from the Jihad.
1. Abu Bakr:
Al-Haakim Al-Nisaboori who is one of the well known Sunni scholars narrated in his famous book Al-Mustadrak Alal Saheehayn, Volume 3, Page 37 that Abu Bakr ran away.
2. Umar:
In Saheeh Bukhari and Dalaa'l Al-Sidq , V. 1, P.362 and Noor Al-Absaar by Shiblanji, P. 87, you find that Umar ran away.
3. Uthman:
Ibn Katheer (student of Ibn Yatmiyyah) mentioned in his books Al-Bidayah Wal Nihayah V.4, P. 28 that Uthman ran away.
Many other Muslims have also run away from the battles due to weakness in the faith. Only the firm and strong in faith stood fast and never ran away.
Exposing the hypocrites was declared in Quran by their deeds but not by their names. Same was done by the Prophet (SAWA) who did not expose their names.
The Prophet (SAWA) has clearly stated that many of his companions will change and turn back from right path after him then will be sent to hellfire. (Saheeh Bukhari, Hadeeth number 4259
and Saheeh Bukhari, Hadeeth number 6098,
and Saheeh Bukhari , Hadeeth number 6099,
and Saheeh Bukhari, Hadeeth number 6026,
and Saheeh Bukhari, Hadeeth number 6528.
Wassalam.
