Our son and daughter-in-law died in a fire apparently without a will. What legally happens and what do we need to do?

I'm so sorry for your loss.  The answer to your question depends on what assets they owned.  To answer this question, you should look at their important papers at home, their mail, and their tax returns.  In general, the law of intestacy applies when someone dies without a Will.  Intestacy provides for estate assets to go to the parents of a deceased person unless the deceased person had children, in which case assets go to the children.  Some assets are distributed by a court-appointed personal representative, so someone needs to apply to probate court for his appointment.  There is an exemption is the deceased person's assets are not worth more than a certain amount (I believe it is $20,000 in Florida) in which case you can use a "small estate affidavit" to transfer title of assets to whomever is entitled to them under the intestacy law.  These forms are available online and probably from the probate court.  Appointment as a personal representative or a small estate affidavit also will gain you access to the safe deposit box, if any, where important papers may be stored and the ability to talk to financial entities about their accounts so that you can figure out what they owned and how they owned it.  Other assets like life insurance, retirement funds, and pay-on-death accounts, are not part of the probate process - you would need to contact the entities holding those assets direclty and provide them with a death certificate.  They then will send claim forms to the named beneficiary and pay that person directly.  If your son and his wife died at roughly the same time, Florida's simultaneous death statute will apply and will divide their probate and jointly owned assets between their estates so that his estate (and so his heirs) will get half as will hers.   I hope the process goes well for you.