Be late for everything. Yell if they're late. Compare and contrast. Go everywhere in groups, especially the bathroom. Do nothing alone.
Independence is a sign of weakness.
Make them guess what you want and then get mad when they're wrong. Plan little relationship anniversaries, i.e. the monthly anniversary of the time you saw each other in the library for five minutes. Then get mad at them for forgetting. Sing all the words. Sing to them.