The short answer is that you need a diode sized for double the highest charge current from the wind generator. As they are charging a battery they will all have a higher voltage than the battery - otherwise no current flows... Depending on the output voltage of each of the generators, the output current will relate to the output voltage, so if one generator has a slightly lower output voltage it will supply slightly less current. Output voltages need to be close, but If they vary by a volt the higher voltage generator will just do a little more of the work.
That's not how I see it operating in practice. If the generators are isolated from each other by simply using 'Diode ORing' isolation to the battery, then the generator with the highest voltage will supply ALL the current flow and cause ALL the other generator's isolation diodes to be reversed biased and turn off ANY current flow from those other generators. Balancing current between separate voltage sources that use simple diode isolation from each other is extremely difficult, as trying to control the output voltage from each generator close enough to try and maintain a balanced current flow would require quite complex current and/or voltage monitoring and some kind of feedback control to the generators or their isolation device to force a balanced current situation between the generators. I would think high current MOSFET transistors might be a better method to allow sharing of current if the proper control algorithm is implemented to adjust the mosfets acting as current controllers?