Can I use 的 between the name and 他们 I had this sentence which was a bit difficult for me to understand at first because of the name + 他们. I understand it now. 

郭高林他们决心用实际行动证明自己。

My questions is, can I write it like this:

郭高林 的 他们决心用实际行动证明自己。
No; in this context 的 is acting as a possessive, e.g. "我的心" means "my heart", and "郭高林的心" means "Guo Gaolin's heart".

他们 means "they" or "them", so it makes no sense to possess this.

The phrase 郭高林他们 means something like "Guo Gaolin et al." or "Guo Gaolin and co." Note no possessives.

Instead, if you want to use 的 you would have to transform the phrase into a possessive, for example 郭高林的小组 (Guo Gaolin's group) or 郭高林的团伙 (Guo Gaolin's team).