set up a project plan... (Score 1)

Set up some sort of project plan or some sort of blueprint of the code that needs to be written for each of the features of the project. If you have already gone through the exercise of writing requirements and a detailed design for the features, this should be a breeze. Once you have this setup, as the lead of the group, you should have a weekly meeting to get status of each of their items on the plan. This way you have everything organized and accountable. During these meetings, you should get the status of each person's sections. If they are late, ask them why and how much more time will be needed for each section. If it lateness still continues, you seem to have a personnel problem and should deal with that accordingly. However, at least now you have a good way of tracking what's going on.