The best way to start out is to develop a robust project communication plan that includes all the stakeholders including the team. What meetings, reports, communications, etc. will be important to keeping them in the loop.
Project conflict is becoming more common as more shortcuts for project management are being taken in the name of cost cutting. These are usually "penny wise and pound foolish" ideas, but it can lead to two team members in conflict. These are the two that can best solve the problem, so a recommended first step would be to chat informally with each and encourage them to get together to resolve their differences.
Of course, if their communication with each other is important to the success of the project, you will need to carefully intervene and possibly facilitate their discussion. Let them know just how important it is that they work together to resolve the issues and make the project successful.
Finally, if that doesn't work, you may need to seek outside help (e.g. from HR). It might also mean that you will need to request that one or both resources be replaced if the project isn't getting the attention it deserves from them. The consequences for the individuals will vary depending on organization (I've been on some teams where if you roll off, you roll out of the company) and you may want to consider how to weave this gently into the earlier conversations as well.