Your insurer will need to evaluate who will be listed as primary drivers and who will be occasional drivers. If you have two cars insured and four people licensed at home, two of those individuals will be primary drivers and the remaining two will be listed as occasional.
If, on the other hand, you have four cars insured and four people licensed, your insurer will typically determine that each licensed driver be the primary driver of at least one vehicle, even if that vehicle is not the one they're primarily driving. Each driver will also be listed as the occasional driver on the remaining three vehicles in which they are not primary.
Keep in mind that every situation is different and there are some exceptions that may need to be factored into your policy. Talk to an insurance advisor for more details on what your insurance policy will look like for you.