[@r-a-y Keymaster 15 years, 3 months ago]

Try the code in this thread to make the forums tab the default group tab:
https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/changing-group-tab-display-defaults#post-55449

Removing the group home tab will probably need some additional code.
Or you can use some CSS to hide it.