Just came back from a three-week backpacking trip with FIVE other people. Trip was just originally just three others (my gf, brother and cousin), but two friends wanted to join. Jesus Christ.
You gotta keep those trips intimate. And preferably, with family. The two add-ons didn't want to do any of the same stuff we did, couldn't keep up, didn't want to try any local food, complained about walking, only packed flip-flops, commented after thirty minutes at the Louvre that it was "just a buncha paintings", etc. etc. etc. Worst mistake. The original squad all chanted "never again" at least fifty times each the entire trip. So yeah. Never again.
Visit my blog too. I thought you may be interested in travel. Nice place @markjastine