Dont rent..Not this trip at least--Hire a driver or get creative with diff.drivers/tour companies (ie clives from negril to MBJ) a driver fro there to Ochi..
If thats too expensive then any reason why maybe you or just a few of you go on this excursion ?? Do all five of need to go??? and yes if you have the time and are very patient you could do some if not all- in route taxis--but going be one looong day... Anyway,could this little child could get closer to one of your destinations (ie maybe you offer to pay for route taxi ) and you could meet them maybe Ochi ??? I'm sorry ,I dont know all of your logistics for this trip..But I say No Way on driving-not until you have more exp.driving there would I undertake this...