The Pink Panther star welcomed her second child, baby daughter May, on 15 January (10) - and three days later, the actress' younger sibling Rosie became mum to son John.
Baby John, who was named after the sisters' late dad, Sir John Mortimer, arrived a day before the first anniversary of the playwright's death (16Jan10).
And the sisters' mother Penelope is glad his legacy will live on through the family's new additions.
She tells Britain's Daily Telegraph, "It has been a very exciting few days. Of course, John died this time last year, so it is just rather a wonderful thing. It does help to think there will be two more of his little grandchildren running around the garden he loved so much. It is really marvellous that life goes on."