For your first question, as per my knowledge, it isn't feasible to share all contacts at once with OCM. We believe that would be a helpful feature if it is developed. In this case, we'd like to suggest you submit your feedback to our related team via the OCM UserVoice here. You can vote or post ideas there. Thanks for your understanding.
For your second question, if you are saying the members in Microsoft Teams, actually, they can export the contacts from OCM and then share the Excel file to Teams with their members. If you are saying his colleagues, actually, when that person shares the contacts, his colleagues should can see the contacts via their OCM.
Feel free to let us know if you need further help.