Breaks are necessary, not just for body functions but to stock up on water and snack breaks. We arrange almost all stops at trailheads, fast-food restaurants or gas stations. I'm not sure of you're route, but most men prefer bathrooms when possible.
Be honest up front about your pace and planned daily mileage. The additions should be willing to stick with you and your friend. There is always the option of scheduling stops to regroup, but on a long ride--everyone should stay together in case of mechanicals or (heaven forbid) accidents. If they don't agree in advance to your pace, then I would consider backing out. There is nothing worse than being left behind, and you can't choose to ride faster than your skill level. Going out hard to keep up will hurt you in a long ride, or multi-day ride.
"Well-behaved women seldom make history." --Laurel Thatcher Ulrich
'09 Trek WSD 2.1 with a Brooks B-68 saddle
'11 Trek WSD Madone 5.2 with Brooks B-17