With a Third House Stellium, you will be an incredibly good networker. You will have many connections that are connected in many different fields in life. You will most likely be able to call up one of your contacts and hook something up if you need to, whenever you need to.
The Third House is the house of siblings and generally, when the person has such strong elements in their third house, it does mean that their siblings play a crucial role in their lives. You could have one or two siblings that influenced you quite significantly throughout your life. Often people with a strong Third House could have shaped their identity through their sibling's help. Your sibling could have helped you become who you are now through teaching you things, or you could have looked at your sibling and adopted certain traits and qualities from them.
With a Third House Stellium, you can sometimes get involved with so many people that there are too many people in your life, and you cannot reach out to all of them, all the time. You are continually meeting new people, and there are always new people coming and going in your life. One thing that is very important with this aspect is you need to identify who it is that you want to keep in your life and who is important; because you can sometimes scatter your energy between many kinds of people.
With this aspect, you must identify who is important to you, and you need to try to keep these people in your life. It would be best if you showed them that you want them in your life because what can happen is you can end up losing the people that are important to you because you are paying attention to people that aren't actually important to you.