All I remember is: a family and their relatives are celebrating something. At the beginning everybody's nice to each other, but then they are trapped inside the house and with time they begin to reveal their "real selves", criticizing each other all the time. I think the film is in Black and White (but I'm not sure). Do you know what film is this?

Thanks!

I wonder if you are thinking about an episode of "The Twilight Zone" called "The Masks," in which an old man who is dying has his heirs all wear masks that reflect their true character:

"Twilight Zone" The Masks (TV episode 1964) - IMDb

Maybe the anniversary (1968)

Can you remember any of the actors? Also, if It's in black and white it would be a fairly old movie.