To a first approximation, if it takes X thrust to stay aloft, the engines produce a combined total of more than 2X, and there is a speed above which the rudder

To a first approximation, if it takes X thrust to stay aloft, the engines produce a combined total of more than 2X, and there is a speed above which the rudder produces enough aerodynamic force to maintain directional control. If you want to get into the nitty gritty, look up multiengine airplane type certification requirements.