To go right off the beaten track for wild camping, you're likely to need a fair bit more kit (like the tents would need to be light enough to carry etc.)
Also, everyone would need to make sure they can hold everything in...or someone's bringing a trowel!
One really important thing is water. Obviously there will be no tap as such on the fells. You could either take enough water to cook with and water the next day but this will be ridiculously heavy. So, plan to camp near a stream (you need fast flowing water; standing/stagnant water is a definite no-go), as high up (near the source) as possible. This should give you plenty of clean water. You can use chlorine tablets to purify if you want (I don't always use them). This will give a slight taste; if that is such a big deal, take neutralising tablets as well (or use Chlorine Dioxide).
Remember that if it is a dry weekend, the streams will be lower.
I would say go for a campsite, especially since the group is so big and if no one has wild camped before.
*disclaimer: Wild camping is still a great way to get out (best of all it's free!), but given the circumstances, you're probably best sticking to a campsite*