The main difference between the 2 groups will be the detail and content of the topics.
Group 2 needs to be a safe place for teens to open up and discuss their experiences and issues without any worry about younger or more innocent girls being present.
Similarly, Group 1 needs to be a safe place for younger more innocent girls to learn about and understand important real life issues that are affecting them or could affect them in future, without being exposed to deeper, heavier and more serious issues the older girls in Group 2 need to discuss.
I need to be able to connect better with the girls in order to help them, which is difficult to do when you have an excited 10 year old girl eager to take part and learn, and a 16 year old young woman in hijab needing to talk about a haram relationship she might be in.
May Allah have mercy on all our daughters and keep them safe.