Glad to help! Scouting has added so much to my girls' lives. Check out this website:
http://www.scoutingweb.com/scoutingweb/index.htm I have no affiliation to it, but it's helped me over the years.That's the kind of thing I meant when I suggested that the co-leader group get together and create a troop plan, which must parents must agree to before they can enroll their daughter in your troop. MOST of the parents in our troop are great people and genuinely want to be helpful and do what's right -- but that doesn't mean that they always know what you expect, and you as the leader have the right to set your own troop rules (within the Safety Wise guidelines, of course).
The biggest issue we had when the girls were younger was late pick ups. Also we had two girls whose mom told them that my rule about parents walking in /signing girls out was silly, and they should just meet her in the parking lot at the end of the meeting (parking lot was not visible at all from the meeting room, so I had no way to know whether they'd made it to their mom).
We take lots of trips, and we've had some parents who've assumed it's fine to include their whole families. Hypothetical example: Let's say we're planning meet at the mall, have lunch, and see the new Harry Potter movie. I've sent out a memo saying, "The trip is $5/person, which includes lunch at Burger King, your movie ticket, and a popcorn." Some families think, "WOW! I'll bring all six people in my family for that price!" They don't realize that this outing really costs more, and I'm able to do it for $5 because the girls just sold cookies, and this is what they wanted to do with some of their profit. That profit belongs to the girls, and I can't use a portion of it to buy movie tickets for their siblings. IF I'm willing to have families along on trips, I'll add at the bottom of the flyer something like "Family members are welcome to come along -- I'm pre-buying tickets for the girls to the 1:30 showing. Your tickets'll be $8. Be sure to allow time to make your purchase." This lets them know that they're on their own (financially) if they want to join us. Other times, I allow moms but not siblings. For example, we did a mother-daughter beach trip once. We chose a house big enough for all the mothers and daughters who'd expressed an interest in the trip, but if we'd allowed siblings, it would've taken away from the mother-daughter aspect of the trip AND it would've made the trip more expensive for everyone ('cause we would've needed a bigger house). The main point: LET PEOPLE KNOW well in advance what you expect for any given trip.
Now that my girls are almost ready to graduate, our leader group always says the same thing to one another: "What do the girls want?" We let them decide whether to include moms, families, whatever. But when they were Brownies, I made the decision, announced it well in advance, and didn't apologize for it.
About money and trips: Always charge SOMETHING for an outing, even if it's just $2. Paying SOMETHING makes the parents stop and think, "Are we free that weekend? Does she really want to go to the nature museum?" On the other hand, if it's a free trip, EVERYONE will sign up, and then half will show up -- and you'll have packed snacks for the whole group and bought tickets for the whole group.
Also be very specific with your instructions/ packing lists for outings: "Meet at the church at 10:00. Wear good walking shoes (tennis shoes or other tie shoes) and bring a light jacket. Bring $5 for lunch. Cameras and phones should be carried in over-the-shoulder purses or fanny packs -- leaders will not carry these for you." Believe me, if you aren't specific, you'll have kids who'll show up in flip-flops (for an outdoor hike) and kids whose parents'll give them $5 at the last minute and never consider that they don't have a pocket. Or kids who'll carry a phone in their hand and lose it within five minutes. You have to think through things for them.
We did have a problem with a sibling being left at meetings once, and -- like you -- we didn't realize it for a while. He was an older brother (maybe 5th-6th grade), and he was left sitting out in the hall outside the meeting room. We meet at a church, and we mistakenly thought his mother was somewhere doing something for the church -- it wasn't 'til the 3rd meeting that we realized he was a scout sibling, and his mother was giving him the choice to sit there and read/play his Gameboy or come grocery shopping with her. We had to confront the mom about this and let her know that IF something happened to him during the meeting, we wouldn't know and that our attention had to be focused on the girls during that meeting. She had just assumed it was okay and that we'd keep an eye on him. She stopped leaving him, but IF she had persisted, I'd have warned her once more and then I would've called the police to report an abandoned child. Yes, I would've lost the scout over that, but that would've been better than that child being injured or abducted (a real possibility where we meet).
The drop-and-run kids don't tend to stay in scouts long, but the ones who do stay tend to have the most thoughtful and helpful moms. The moms who say, "Oh, you're doing a walking photography tour of downtown? Well then you need some extra help. I'll come along and stay at the back of the pack to prevent stragglers." Or "A zoo trip? I can't drive that Saturday, but I'll send a cooler of juice boxes."
Final thought: At your beginning-of-the-year mandatory parent meeting, ask the parents what resources they might have to help the troop. If one of your dads is a fireman, he might set up a firehouse tour for you. If one of your moms is a nurse, she might be very willing to do a one-time program for you on first aid. Between all your scouts' families, you probably have some great resources. Make it very clear that you very much welcome one-time leaders, people who don't want to take on the responsibility of leading week-to-week, but who'd love to put together ONE meeting to teach the girls how to can pickles or put together the activities for the Manners Try It.
And sometimes parents come up with great things you don't expect: One of our moms once won a bowling party at a local spot, and she donated it to our troop. It was a great outing and we just paid for a few pitchers of soda.
She just doesn't like to play tag like most of the other kids do. She would rather pretend play and it seems like most of the kids want to run around and chase each other instead. 
