(Due to reputation<50, I cannot comment) What is the constellation in your group and the other group (PhD student, post-doc, professor, ...) and how well do you know each other?
First of all, you have to have a consistent opinion within your group about whether the references are indeed irrelevant self-citations only to pump up some citation counts or not. By discussing this issue with your group leader (assuming you are the PhD student/post-doc in your group), you will get a feeling whether confrontation must be avoided at all cost or your group leader will back you up on this issue.
Then, consider politely asking the co-authors to reconsider the references list. Point out to the guidelines of the journal and/or of our university that state address citations. While this answer is not creative and you surely have thought of this one yourself, it is the honest approach which will define the framework for the future publications this collaboration will hopefully yield.