If you are group of 40 people then "Dagri Banglow" trek is strongly recommended only.
Your route will be like this :
Murree---Nathyagali (Approx 2 hrs drive)----Meeranjani top (Approx 2 hrs steep trek)-----Dagri Banglow (1.5 hr Normal but very beautiful trek)
1) You have to reach Nathyagali by 11 am maximum
2) You have to depart for trek not later then 1 pm
3) you need to carry water upto meeran jaani
4) Water is available in Dagri Banglow
5)2 rooms can also be available in dagri Banglow
6) Yes, tents and sleeping bags can be available on rent from Islamabad
7) You need horses for your belongings, a single horse will cost you 8,000----10,000.
Hurry up........