VIC What mistakes would constitute a Will as invalid?

[Ziggy Fischer]

What are the most obvious mistakes in a Will that would make it invalid? I have heard people adding handwritten notes on the actual Will will do it. In my case, there are 4 recipients and 2 brothers have mistakenly given the same middle name on nearly every page of the document, would this make the Will invalid. Could it be argued that a very old man who could not see that the bolded names are simply incorrect may not then have understood the finer points of the document such as the percentages?
Also, a granddaughter's name uses a nickname and the deceased daughter has had her last name is spelled incorrectly, "Dole" instead of "Doolan".

Thanks any advice would be appreciated.