M.
I haven't dealt with it, as my daughters are 2.5yrs. apart and the youngest is just a year old. However, I think it's wonderful that your two want to be together. I see no reason to push the issue of alone time with either you or your husband if they don't want it. However, you may want to consider enrolling each of them in a seperate activity class of some sort through your parks & rec department just to start getting them comfortable with being apart from one another. But with two years to go before the oldest goes to school, there is no hurry.