Referring to papers by myself and others in my thesis
Personally I feel (and I know that there are many who might disagree) that it is perfectly fine to use 'I' and 'we' here. I think that obsessively sticking to passive voice makes papers and theses less readable. After all, you did do the work. Why hide behind the passive voice? My suggestion would be to go with option 2:


  Together with B and C, we showed that this can be done [ABC15].