In this paper, we describe a Human-Robot Interface (HRI) software architecture designed to enable teams of operators to share tasking for multiple unmanned vehicles and systems. Many existing robotic systems are controlled using specially-designed interfaces, which becomes problematic for operator teams controlling multiple heterogeneous systems. We propose a solution that enables teams of operators to control multiple heterogeneous vehicles and systems using a common command and control environment. This environment supports task sharing and handoff and was shown in evaluations to improve team efficiency.