Over the 24 episodes of The Persuaders, many members of Brett Sinclairs family were either alluded to or actually seen during the course of various episodes.

Surprisingly, the genealogy mapped-out via Brett's stories of dubious authenticity, seemingly designed to annoy Danny Wilde, is reasonably consistent and only 1 error over the series is recorded.

Brett's ancestor stories not only provide comic relief  but  the continual reference to members of his family, past and present adds dimension to the character, endearing Moore's Lord Sinclair to viewers. A Death in the Family is a story which deals entirely with the larger Sinclair clan and remains one of the best loved episodes of The Persuaders.

The table below is a list of all Sinclair family members that I are mentioned across the series' 24 episodes with their respective relationships to Brett and places in the Sinclair heirachy.

Some of the names are 'linked' to an illustrated transcript of the associated story of that particular forebear.

If there are any relations I have missed, please let me know.

 
UNCLES
 
Sir Rodney Parkington-Sinclair (The Ozerov Inheritance)
Diarist acknowledged as one of the most boring men in the World. One of his diaries provided the evidence that could prove the Ozerov claim on the Crown jewels of the exiled Ozerovs. 
The Viscount Chesterfield (The Gold Napoleon)
The Duke of Caith (A Death in the Family)
Holder of the family title at the time of the family killings 
Sir Angus Sinclair (A Death in the Family)
3rd in line for the family title. A Scottish Laird with a taste for haggis and  a passion for playing the bagpipes - Squashed to death by big gate from which Roland Sinclair had removed the hinge-bolts 
Sir Randolph Sinclair-Strathers (A Death in the Family)
(aka The General) 
4th in line for the family title and 1st victim of Roland Sinclair. Killed by exploding model tank.
Admiral Horatio Sinclair-Hawkins (A Death in the Family)
5th in line for the family title. 2nd victim of Roland Sinclair. Killed by exploding model ship
Lance Sinclair-Boswell  (A Death in the Family)
6th in line for the family title drowned in vat of wine. Lance had inherited several distilleries a few years earlier and had been drinking their combined output ever since. His goal was to find the perfect wine - which he eventually discovered but unfortunately he was drowning in it at the time. Last words: "Eureka! That's the one!" 
Percival Sinclair(A Death in the Family)
Tenant of the coffin Danny and Kate sit on in the family crypt 
The 16th Duke  (Anyone Can Play)
A great-great uncle alluded to in one of Brett's family stories. 1 of 2 stories that were recounted to someone other than Danny and the only one not related in its entirety. Brett is unsure as to whether the story is about the 16th or 17th Duke but goes on as if it was the 16th. 
Uncle Charles (The Old, the New and the Deadly)
Collector of Rolls-Royce cars and wives. He has14 of both. 
Un-named Uncle (Chain of Events)
Owner of land on which Brett & Danny pitch camp for their 'back to nature' holiday 
The Viscount Eckersley  (To the Death, Baby)
A great-great uncle on mothers side - the man reputed to have made the worlds largest wager on a hand of cards. 
AUNTS
Lady Agatha Sinclair-Boswell(A Death in the Family)
Sister of Lance who bears an uncanny resemblance to Brett
COUSINS
Onslow Sinclair-Lumsden(A Death in the Family)
7th in line for family title. Killed by fatal voltage from guitar
Roland Sinclair-Timberly(A Death in the Family)
The Australian branch of the family and 8th in line for the title. Hatched a plan to kill all the Sinclairs who stood between himself and the title. Killed by the bomb he himself set to destroy the crypt.
Wigham Sinclair-Strathers(A Death in the Family)
14th in line for family title. Suspected by the Duke of Caith as being the perpetrator of the family killings as he neither smoked nor drank or went with women so therefore could not be trusted 
Kate Sinclair (A Death in the Family)
Writer of detective novels and co-investigator of family murders
Un-named cousin #1(Read & Destroy)
Owner of the country house that Brett sends Felix Meadowes to stay 
Un-named cousin #2(Greensleeves)
relative who wandered about the secret passages of Greensleeves for "weeks and weeks" 
COUSINS REMOVED
Archibald Sinclair-Beauchamp(The Man in the Middle)
A distant cousin but never distant enough according to Brett.
Winslow Sinclair-? (A Death in the Family)
3rd cousin and 137th in line for the family title 
DIRECT-LINE
Bretts Father - the 14th Earl of Marnock  (Greensleeves)
Seen only in a photograph. As the 14th Earl was not targetted in "A Death in the Family", it must be assumed he had either already passed-on or had relinquished the title to Brett
Grandfather - the 13th Earl of Marnock  (The Ozerov Inheritance)
Alluded to by Grand Duchess Ozerov -  she had met him at the Russian court before the revolution 
Great-Great-Grandfather - the 7th Earl of Marnock  (Five Miles to Midnight)
Killed while on service in India during the mutiny 
Great-Great-Great Maternal Grandfather - the 7th Duke of Wendleshire  (Someone Waiting)
Used by Brett in a story to convince Danny of the importance of a healthy breakfast. The Duke died of excess at the age of 24 and has the distinction of being the youngest Duke in the family vaults 
UNKNOWN RELATIONSHIPS
The Marquis of Castlehare  (The Old,the New and the Deadly)
executed in France during the revolution due to an unfortunate case of mistaken identity - he bore an uncanny resemblance to Louis XV 
The 3rd Earl of Marnock(Greensleeves)
died at the age of 3 and was the only Earl not to have his portrait painted. It was this tidbit of family knowledge that exposed Brett as the 'real' Brett Sinclair as it wasn't written-up in any of the history books 
Un-named ancestor  (Greensleeves)
Brett claims this ancestor lured the lover of his wife into the secret catacombs beneath Greensleeves to get him drunk and wall him up in an alcove. But the plan went horribly wrong when the ancestor himself became so drunk, he bricked himself-in by mistake. 
Young Master Reginald(Greensleeves)
Alluded to by Moorehead the butler. The recipient of a nasty accident.

In Someone Waiting, Brett tells Danny that his Great-Great-Great maternal Grandfather, the 7th Duke of Wendleshire, died at the age of 24 therefore having the distinction of becoming the youngest Sinclair in the family vaults. Yet in Greensleeves Brett mentions the 3rd Earl of Marnock who died aged three years.