HELP! 90 minute Group Presentation!

[happyhelper]

I am studying Nursing and we have just been given a brief for an assignment, which is to be a 90 minute (Yes! 90 minute!!) group presentation. We are a group of 14 students and obviously all need to have an input into the presentation which is to be in front of approx 50 other students and 3-4 lecturers.
We can present in any style, be it like a standard lecture or play using props etc. We have been given a scenario and have to analyse two characters from a biological, nursing and psychological view. A majority of the group want to do it in a jokey big brother style play.
The problem we have is that none of the group is confident enough to stand out as a team leader to help co-ordinate the planning/organisation of the presentation so we are all going round in circles with no real direction. In turn many members of the group are getting frustrated. Another problem is that due to the lack of confidence the group members have, a few of us feel that a play that is meant to be funny won’t work as there are no ‘dramatic’ show-offy people so it will turn into a dismal attempt at humour and wind up being a boring flop!
Does anyone have any ideas on how we can gain structure and direction in order to produce an informative and intersting presentation (bearing in mind we have to keep the presentation going for 90 minutes!!)
Thanks!