There is an airport train that circles around the airport terminals, so one group can ride that to meet up with the other group at the other terminal. It's a free train. As far as a transport company, you can take Super Shuttle or another bus service, but it would likely be cheaper to take two taxis or a car service to the city. A taxi is typically around $45 plus tip, and car service is around $60 plus tip. Super Shuttle charges $15 per passenger, and you often have to wait for other people in the shuttle to be dropped off first, depending on where your hotel is located.
Have fun!
There is an airport train