I would be more compelled to call it a group, rather than a coven, seeing as you only have 4 members including yourself.
If you would like to create a bi-weekly newsletter to send to the 3 other members you could use a template available in Microsoft Word or Microsoft Publisher. Additionally I'm sure you could find something of use on the internet for free if Microsoft programs aren't available.
I would suggest your 'coven' (group) is focused primarily on the study of magick, rather than practicing as I am assuming the members are inexperienced. If this is the route you wish to follow, then I recommend adding only spells created by the members of the group to the group spell book or 'Book of Shadows.'
This following part is just my little schpeal on the subject, feel free to disregard it if you choose:
I've found that these and similar groups typically lose momentum after a week or two and are soon left in the dust. It's not always easy to maintain such a group, and often members will stray once the general excitement of it's creation dies down. Although I would be happy to see such a group take off, my advice is to not be discouraged if such a group is to fall apart. Just save what work was completed, and perhaps it can be used for another day sometime in the future.
Best wishes, and good luck. If your group needs anything you are free to send me a message.