If they take both then :
- They have taken with them more of their belongings. A car is too expensive to leave behind.
- IF disasster is very bad and return will take some time, they may even sell small car and rent a flat with the money.
- If disaster is a small one and temporary, two cars will offer enough space for sleeping/camping. Two cars with loaded roof tops will make such a bug out trip like a comfortable picnic.
On the negative side for having two cars:
- In a messy bug out trip with broken communication lines, the family maybe separated.
- If one is a 4x4 and the other car is a small compact car, a point in the road may dictate ditching the smaller one which cannot proceed any more. In such case leaving it at home may have been wiser.