Usually when you sign up for a reward campaign, the total amount allocated for that type of campaign is shared among all participants, but if it's a signing campaign, it also takes into account the rank you have on the bitcointalk forum . When you enter the project page where you want to participate, there will be listed for each rank, how many stakes are allotted. The higher your rank, the more you get more money. In conclusion, the total amount allocated to the bounty campaign is not shared by the participants, but other factors are also taken into account.
Normally, it will not be shared equally, unless you all have the same stakes over all, which we know stakes are shared based on ranks and there cannot be a single rank only in a campaign, so this is then shared based on the total stakes helped by each person.