Learning with others usually only helps you unless they are disruptive and not really trying to study with you.
If your colleagues are dedicated into learning a new language together and you are comfortable with that, then go for it! Like with classrooms, there are multiple students that each have their own weaknesses and strengths that can cover each others. For example, if you are weak at verb tenses but strong at grammar, you can help others improve their grammar while they help you improve your verb tense knowledge.
This can be reflected off this Stanford paper:
...it offers students the opportunity to learn from each other. It gives them considerably more practice than traditional teaching and learning methods in taking responsibility for their own learning and, more generally, learning how to learn. It is not a substitute for teaching and activities designed and conducted by staff members, but an important addition to the repertoire of teaching and learning activities that can enhance the quality of education.
Reciprocal peer learning emphasizes students simultaneously learning and contributing to other students' learning. Such communication is based on mutual experience and so they are better able to make equal contributions. It more closely approximates to Habermas' notion of an 'ideal speech act' in which issues of power and domination are less prominent than when one party has a designated 'teaching' role and thus takes on a particular kind of authority for the duration of the activity.
Unless you feel you will not benefit from the group, join them!