BuddyPress.org

Please don’t bump your posts more than once every 24 hours.

You can remove the sidebar on individual group pages by modifying the groups/single/home.php template in your child theme. (If you don’t have a child theme, see https://codex.buddypress.org/theme-development/building-a-buddypress-child-theme/) The sidebar file is included near the bottom – just delete those lines.

You can reduce the font using css. All groups pages have the body class “groups”, which should make it pretty easy to specify that you only want to change font sizes on those pages.