Trends over time tend to be best represented by line graphs. Total membership trends, or for Eastern and Northern on one graph, I would go with a line graph in both cases. For the latter, I would include a legend that runs close to the end of the lines at the right of the chart.
To compare total membership versus employee/spouse/dependent would depend on what you were trying to gauge from the data. If you want a visual of total membership, and how much of that total is comprised of employee/spouse/dependent, a stacked line graph may be a good option. Alternatively, if what you want to visualize is the hard trends for each category, a bar graph or a composite bar and line graph (line representing total, and bars representing the separate components) may work better.