Squirrels in your attic can be a dangerous situation. They can chew wires and start fires but usually they just destroy insulation and chew holes for entry and exit points. Usually cages set over the holes where they are entering and exiting is the best practice for catching and removing them. I believe that you should remove the squirrels that have made your attic their home instead of simply excluding them because they often move around the other side of the house and chew a new hole.
Usually my service is three parts, first I come out and inspect the area, including the attic, roof, and soffits. After determining the areas of intrusion cages are installed over the holes preventing further entry and catching any squirrels that try to enter or leave. I remove all squirrels that are caught and when we have them all I take down my cages and give you a quote to seal up the area preventing any future occurrence. If you choose to have me seal the area I offer a warranty on my work that a squirrel will not get through that specific area.