Remove "Order by" in BuddyPress Member List?

Hi all -

I've got a client that wants me to remove the "Order by" options in the buddypress and only use the alphabetical listings (they don't want members to know who's been active, or newest registered) and I've been searching, but I don't know where to find that. Does anyone know how to access that functionality?

Additionally, they want the alphabetical listing by LAST NAME, not the default way (which I think is by username? I'm not sure)

Any insight would be so greatly appreciated!