I did have a massive row with a creditor when the mother-in-law died owing for a new mattress she had ordered the week before she died (which they tried to deliver the day before the funeral which didn't help). In the end I used a free 30 minute consultation advertised by a local solicitor, who...
The undertakers would be able to advise about funeral costs and how to pay them. I found them very helpful when my Dad died (all be it eyewateringly expensive).
I think you need to talk to a solicitor as well as CAB.
The debts will probably netted off the value of the estate during probate, but I don't think the creditors can come after the relatives if the estate can't afford to pay them unless the relatives are also named as joint debtors on the...