What Olivia says is really the key to your question.

You have limited time in St. Petersburg. You want to make the most of that time. You do not want to spend it in line waiting to get into an attraction (believe me, the lines can be long!), and certainly not waiting for others at bathroom or "shopping" stops.

You mentioned that there will be eight of you. I would think that a mini-van can be arranged through Red October. For a first visit they will know what you should and can see within your time frame.

Within your private party you can use a cattle prod to keep your group on track and moving, or slow down and take time as you see fit.