You'd need to check the specifications for both the Jeep rims and the Pontiac van's wheel hubs to see if they are compatible. This information is often found on the wheels themselves, in the owner's manuals, or via online resources. Even if the bolt patterns match, the offset (how far the wheel mounts in or out from the hub) might be different, potentially causing problems with rubbing or improper wheel alignment.
In short: Don't assume they will fit. Always verify compatibility before attempting to mount any wheel on a vehicle. Incorrectly fitted wheels can lead to dangerous handling and potential accidents.