According to Croatian law, at least one person on board must own a navigation and VHF license. If it is not the case, then you should hire a skipper who has all the necessary documents. These documents are issued in Croatia in Harbor Master, after attending a course and examination in navigation and radio telephony.
If you have these documents and they have been issued abroad, please check whether they are valid in the Croatian territorial waters. If you want to rent a boat without a crew, you must send in advance a copy of your navigation license in order to have your booking reservation confirmed. You must have the original documents with you on board. Croatian laws are very strict in this regard. If you rent a skipper with a valid license, then your group should have only passports or identity cards.