Along this same line of questioning. When neutrals retreat to an adjacent area can they move to an area containing other neutral units of a same type, or does the area that they are retreating to have to be uncontrolled.
An uncontrolled area is simply an area that is not controlled by another player (remembering that home areas and areas with strongholds are controlled areas, even if there are no units there). An uncontrolled area may contain cities or neutral units. It is up to the player controlling the neutral units as to which area the neutral units retreat to, if there is a choice (say between an area that is completely empty and an area that already has a neutral unit). Different types of neutral units can be combined together in the same area, they are all of the same neutral "faction".