Officers investigating the discovery of three bodies at the foot of the White Cliffs are appealing for help tracing the last movements of the brother and sister by speaking to hoteliers and B&B owners.
Formal identification has not taken place but police believe they were twins, aged 59, from the Elton area of Cheshire.
The body of another man was also discovered in the same spot in Langdon Bay on New Year's Day. It has been identified as a 45-year-old from Manchester.
None of the deaths are being treated as suspicious.
Detective Sergeant Stuart Ward said: "We know they were in London on 22 December and we can place them in Dover on Boxing Day, but we are keen to establish if they were staying locally.
"We have already contacted local hotels but are now asking owners of guest houses, bed and breakfasts and pubs to contact us if they had a man and woman in their late 50s from Cheshire staying over the Christmas and New Year period."
Officers would also like to hear from anyone who saw the pair, who were wearing dark-coloured wet weather clothing, at the top of the cliffs in the period between Boxing Day and New Year’s Day.
A report is being compiled for the coroner looking into the death of the 45-year-old man from Manchester.
His next of kin have been informed.
Police are satisfied that the deaths of the second man and woman are not connected to the death of the first man.
If you have any information that could help with the enquiry please phone Kent Police on 101 quoting reference number 01-0980.