You must leave the sterile area to change terminals. There is light rail between the terminals.
Will you be renting a car? If you have a checked bag you will need to stow it somewhere. Tell the rental car people of your plans so they will know that the car will stay there a while. If no car you may need to ask the WN baggage people to hold it in the baggage office next to the bag carousel.
Once you are free of any checked luggage (or any extra stuff if renting a car) you can go to the United ticketing in T1 and ask for a gate pass saying you want to meet friends in the lounge. It may or may not be a problem. You might want to call ahead first.
If you are renting a car, you might want to make your reservation for T1 so you will be close to your car after your meeting.