I clearly have a warped sense of the value of the sibling relationship. Maybe that's why I looked at people in confusion when they acted horrified that I didn't want to "give Caroline a brother or sister". I'm wondering if I love my sister too little or something.
To me it doesn't seem like it will cause long term harm to separate siblings at the ages of 2 and 4 if there wasn't a home that could take both of them. They clearly have already spent a lot of time apart. Ideally they would be kept in touch with one another and could build as much of a relationship as they chose to.