They all have big noses. All of them have big noses.

xiaokaoy, You are asking about subject compliment agreement. Here is my opinion. Each of them has a big nose. This is the clearest in meaning. The other two are also correct and are usually understood to have the same meaning in context as "Each of them" but with a different emphasis. -All of them have a big nose. Here you are stressing the word "nose". -All of them have big noses. Generally, it is better to use a plural object with a plural subject. The problem is that we don't have a neutral third person singular pronoun in English. We should have one, but we don't. For example, All of them have a big nose. Does this mean there is only one nose for all of them? All of them have big noses. Does this mean everyone has several noses? All of them have their big nose. Does this mean there is one big collective nose? All of them have their big noses. Does this mean everyone has several noses?

Sorry to be completely unhelpful and silly but your question made me think of this... http://youtu.be/Ahg2GVWHGKY