There is a PDF form you can print out from the website, and mail in.The cost is $5.00 for each death certificate, and it usually takes a couple of weeks to get a reply from the state.You have to send each request separately.
Of course they will need as much information as possible for each request, but the minimum information required is the name, and year of death.
Obituaries may also help you find the cemeteries. Using the University of Florida’s awesome collection of Florida newspapers I do obituary lookups, but not as a volunteer. If you are willing to reimburse me for a trip to the library, I would be willing to do a search for some obituaries.But, I would need full dates of deaths for all three folks you've mentioned. You may still have to send off for a couple of death certificates in order to get the full dates of death.
If you would like my help with the obits send an e-mail to firstname.lastname@example.org