In the day-to-day reality of working in a company, sending an email to one person is not as common as to two or more people. However, it is different to know how to communicate to one person than to know how to communicate to a group.
Should you be more careful not to offend anyone? Or maybe you should rather focus on making the information understandable for everyone. Or perhaps both? The chances that you will be fully aware of who has what communication preferences are slim. And even apart from that – choosing the right communication style will be very difficult.
So best to leave it to Em. She will easily process information about each person and choose the appropriate communication strategy for the whole group.