According to the official IMDB page of the Supergirl television series, both Helen Slater and Dean Cain are listed as Kara’s adopted Earth parents, Sylvia Danvers and Fred Danvers.
Though as the source of this news pointed out, IMDB can’t always be trusted.
The Internet Movie Database isn’t always accurate, as some submissions could come from a fan’s overzealous wishful thinking…
However, sometimes managers are the ones making submissions, and they don’t try to hide casting surprises and things like that.
Grain of salt shall be taken with this report, but at the same time it makes sense, it’s be perfect casting and it’s an awesome homepage!