The link is ok and doesn't need any diodes. You will likely end up with one battery more charged than the other and to work properly you would need a 12v charge controller for each battery ( twice the expense).

You only gain if you are using something that is not really suitable in the first place. If you are using tape motors or something it may help.

If you build something sensible and build it right you will gain nothing over using a 24 v machine direct. You can parallel multiple 24v machines if you want to and use one charge controller.

I am not sure if your plan was to connect the two machines directly to 24v in high wind. If so you would have a simpler arrangement with just 24v and using series/parallel or star delta to match for high and low wind.

In UTAH and in South America there are several sites that have small wind mill ( using heavy truck fan radiators motors), one of them charges a 144 volts bank with 16 wind mills -- low cost indeed -- almost nothing -- the owner got pipes and wood and motors free or almost free.

He has one of my DC/AC transformerless MSW inverter.

The fellow in UTAH place several in series and he has told me that the motors last about 4 to 6 years -- the blades are very easy to make - I do not recall the diameter --.