45-60 min drive, depending on traffic, and whether or not you choose to take express lanes for $10-$15. There is a 75-90 min bus for $11 that runs regularly, from the airport to downtown Boulder. Use the RTD website or app to check the schedule and purchase tickets.
Not necessarily, although it would offer you more convenience. Pearl St Mall (downtown Boulder) is very walkable—including trails!—should you book accommodations there. The venue is a 10 min drive or Uber ride from the Pearl St. Mall.
YES! Your kids are most welcome at the wedding and Sunday gathering.