The way that I see it is that a coven is like a family... there are times for social fun, and times for serious practice. You can't really change how others feel. If they aren't serious about the craft, then you can't really make them be. Its a lesson I learned early on in my group. We totally could party the night away.....AFTER ritual. We have the mirth post reverence.. thats not to say that our rituals are always serious, but we have structure and that seemed to help.
Leaders who ban things sometimes can seem a little power-trippy. If I want to have a glass of wine post-ritual with my covenmates, I don't think that should be disallowed- its like saying I can't control myself. I wouldn't ban, merely shift. Sometimes alcohol can also be helpful prior to ritual, depending on the intent of ritual. As a group, in the past, we've done ritual after a round of shots. I understand what you are trying to do... if I were in your shoes, though, I wouldn't start banning things, I feel like that might be treating the symptoms and not the actual illness.
Without the training and workshops, and other magickal educational things we make a priority, I think we'd be a little unfocused as well. Shared educational opportunities really helped us focus and bond well as a group- especially those where everyone had to contribute to the lesson.
Here are my non-ritual suggestions:
~create structure within your group- if you don't have a set of bylaws, make one. We use this as the document we all refer to.
~in regards to ritual time, to get everyone focused, I suggest having a gather at X, circle at X starting time. We usually gather at 6, circle at 7. This gives us a chance to get the sillies out, discuss the ritual, and set up.
~do some serious training, do some energy work- practice drawing energy, passing it around, that sort of thing. It can get really fun and will help y'all get more in tune with eachother while practicing drawing energy.
~set a serious tone- silence can be deafening. And it works sometimes. Or drumming. If someone is being particularly distracting, give them a part in the ritual. Ask them to be the drummer, or call a quarter or something. I don't really know how your rituals shake out- how involved the rest of your peeps are, but I've found this to be helpful
~get someone else on the same page as you, and ask them to help you keep everyone focused on whatever task is at hand.
~take deep breaths together and do a grounding exercise pre-ritual.. I like to ask someone else to lead this one.
~as part of your circle opening (if thats how you roll), create something that everyone can say together. I cast the circle in my group (usually) but there is a short piece of prose we all say post-circle cast, pre-quarter call, and it ties us together and helps us focus.
For Samhain, you might want to do something serious... one idea is to take time in the ritual to write a letter to a loved one who has passed over. Those letters are read aloud by the writer, then caught on fire and placed in a cauldron in the center- the smoke carries our words to our ancestors. Then followed by a guided meditation to communicate with that ancestor. It's very emotional and very serious. And a bonding experience as everyone supports everyone else. We definitely need vino after that one!
It just doesn't sound like your group is all on the same page. It might be a good idea to have a discussion at your next meeting about what they want out of a coven. Explain what your expectations of the group are, and ask them if thats something that they think they can try to fulfill.
How many are in your group?
What's the joining process- are you pretty structured with dedication/initation rites, or is it a pretty inclusive group?
If I think of more ideas, I'll post them.