How do I email all members in a Workspace group as a combined group and not just the group's email address?

I have just started using Google Workspace for non-profits as admin and am writing up introductory notes for the charity's trustees partly to persuade them that it's a good idea to use this system, rather than a mixture of email, WhatsApp and text messages.

I am trying to find out how to email a workspace group from Gmail. I have set up two groups: one called 'Trustees' and one called 'General'. I'm not in the Trustees group but I have four test users in the General group and have also added the 'All users' contact which should allow me to contact everyone.

How can I do this for all members of a specific group only - in this case, Trustees?

What do I need to do?