Using Bramble normally, you can teach up to 4 students at once in a Room (plus yourself). Just send them all the same Room link and you will all be joined in the Room together.
To make your group sessions even more effective, try out our new Birds Eye View mode. This allows students to be split up to work separately whilst the tutor has an overview of what all students are working on at once. Find out more about how that works here.
We have also introduced a broadcast mode which enables a single educator to teach 20-30 students at a time. This isn't like a chaotic conference call with 30 people on it but more akin to teaching on a whiteboard whilst talking through concepts. It also uses considerably less bandwidth. You can find out more about it here.