Are team members battling it out to get what they personally care about most? Are you as project manager trying mightily to reach a consensus decision that will give everyone what they most want—make everyone happy? Or is everyone truly focused on what is best for the company? The latter might involve people having to "give" on some pet items for the overall good of the project.
Some companies have a culture of driving to full consensus on all decisions, willing to spend the additional time to review and re-evaluate options and issues until everyone on the team agrees on every item. This may work in some environments, but it can also be unproductive in the grand project scheme, robbing precious time from achieving the most important objectives while everyone tries to reach full agreement on smaller matters. Decisions are hard to make, but they must be made in a timely manner.
Overall, your role as project manager should be to lead the team through tough decision-making for the good of the project—meeting its most important business objectives for good of the company. Whether you make the final decision yourself or have to get an executive to make the call, the team must ultimately buy in to the decisions made, so they'll support them and stick to those decisions during the project. If your team members understand the reasons for the tradeoffs, and why they're best for the business at this time, they're better able to live with those tradeoffs, even if it means leaving out some things they'd really like to include in the project.
The process for getting to the right tradeoffs can build that buy-in, by involving the team in identifying and analyzing alternatives. A Flexibility Matrix is a good first step toward understanding what's most important. Is it critical to meet a specific schedule date? Hold the resources and associated project costs to a certain level? Achieve a specific feature set or scope that's critical to satisfying the customer? Have the team use the matrix together in a team meeting and identify what can't move, what could be adjusted somewhat, and what can "float" to allow the other important parameters to be met. Then the team can identify alternatives within those constraints and use a Project Alternatives Tradeoff Table to document and communicate those options.
Beyond using this process to identify and analyze tradeoff options, you also need to know if you are the decision maker for these tradeoffs—and if not, who is. Typically the decision maker for large strategic project tradeoffs would be the executive sponsor. Decisions must be made with the organization's business objectives in mind, by someone with the authority to make the tough calls. So if you don't get to make the decision yourself, you can review the options with the team and make recommendations to the sponsor as to which option best meets the business objectives. And whatever decision the executives make, the team should hear the executive rationale. Between participating in the alternatives analysis and hearing any final executive reasoning for their final decision, the team should emerge from this process with buy-in to the "right" decision for this project.
For more thoughts on this common problem, read our related articles about decision-making, "Decisions, Decisions", and "When No One Can Decide".
You can also take a look also at our guidelines on what the Project Sponsor role and responsibilities are meant to be, to make sure you're getting the decision-making support you need from company executives.