I would use a line graph to track the Flores Del Mundo membership over the course of a year. A line graph is best at simply looking at chronological trends.
If we were to change it to look at membership between employee, spouses, and dependents, I would most likely use a bar graph. Bar graphs are great for comparing categorical data.
If I want to show membership of employees, spouses, and dependents on the same graph, I may use a bar graph with sub groups, and the two sub groups would be the two zones.