While watching the King’s Speech (as HBO tells me it’s leaving the HBO app, they clearly know their punters I had no real desire to rewatch before that 
) I realize Helena Bonham Carter plays the duchess of York (and future queen mother) in that film and went in to play her daughter Princess Margret in the Crown.
Any other examples of this?
If not limited to separate productions, George Arliss played Mayer Rothschild and his son Nathan in The House of Rothschild (1934).
Patrick Stewart played Henry II in the 2003 TV version of The Lion in Winter and Richard I in Robin Hood: Men in Tights.
The Royals have a wealth of this. Helen Mirren has played both Elizabeth I and Elizabeth II.
But Elizabeth II is not descended fro Elizabeth I, so does that count as two generations?
They are 1st cousins, either 13 or 14 times removed, depending on whom you ask (according to google). I’m also not sure if that counts or not.
1st cousins (once removed) are different generations (that’s what the removed indicates), but not directly connected…
Brian
And her on-screen sister, Olivia Colman, had also previously played their mother in Hyde Park on Hudson.
Vanessa Redgrave was Anne Boleyn in A Man for All Seasons and Elizabeth I in Anonymous. (And she was Mary, Queen of Scots.) Rupert Everett was Charles I in To Kill a King and then was Charles II in his next film, Stage Beauty. In The Young Victoria, Jim Broadbent played William IV, having previously been Prince Albert in Blackadder, while his on-screen wife, Harriet Walter, subsequently played his grandmother, Princess Augusta, in A Royal Affair.
For the classier type of British actors, this game isn’t too difficult to play.
The convoluted inbreeding of the royal lineage suggests yes.
Related, not descended. Elizabeth I didn’t have any children.
In the comedy department - didn’t Dick Van Dyke play Old Mr. Dawes in the original Mary Poppins and his son Mr. Dawes Jr. in Mary Poppins Returns?
The OP specifies “real people”, though.
A bright line not to be crossed, though you must admit that the portrayals of many historical figures are pretty darn fictional.
Ralph Finnes 3-generational in 1999’s Sunshine is a fiction, but borrows much from the real person of Attila Petschauer. Not a great movie but not a bad one, but its main virtue is that, a Hungarian production, admits to their own involvement in the same events of which they were also the victims.
Geraldine Chaplin played her own grandmother in Chaplin. She also is listed in the IMDB as playing herself.
ISTR Michael Palin doing that too.
William Daniels famously played John Adams and less-famously played John Quincy Adams.
Twice!
He also played Sam Adams. And he played John Adams more than once. Daniels had a lock on the Adams family.