The first (and, if I'm not mistaken, the only) mother and daughter pair to earn Oscar nominations for the same film: Rambling Rose, for which Laura Dern was nominated as Best Actress and Diane Ladd as Best Supporting Actress. Hard to argue with that.
In a word? Magnifique. For proof see any of the number of films they've made together - I recommend A Christmas Tale (though the animated Persepolis, in which they both perform voice work, is also an excellent choice).
Still hard to believe that both are gone and in such quick succession, but there can be no doubt about the impact each had on Hollywood history and pop culture.
Two great actresses, though while Ingrid Bergman was a classic Hollywood star with 3 Oscars to her career, daughter Isabella Rossellini has had a more eclectic and off-center career.
It's not all that rare for two members of a family to become stars, but it's a pretty special thing when two members become genuine icons. For that reason, there's no beating Judy and Liza.