This is a movie I remember seeing as a kid – probably in the mid-80s or so. However, I think the movie is much older than that, as it’s in black and white. I saw it on TV, and it was in English, but I have no idea about the title at all.
Anyway, what I remember is that it’s about a couple of kids. In their house, they have both a cat and a dog. Somewhere in the movie, the dog turns into a somewhat ghost-like lady of light who is trying to help the kids as much as she can with whatever it is they’re doing (and I really don’t remember what sort of “task” they had/what the plot was about), but I’m unsure whether the kids are aware that the lady of light is really their dog, as they also see just the dog sometimes. Similarly, the cat also turns into a lady at some point, but this one appears to be a direct counterpart to the lady of light, and she is constantly up to something evil, trying to deter the “good” plans. I especially remember a scene where something is supposed to happen at midnight (unless it gets prevented by then?), and the cat lady goes to tinker with a big clock (on a church? near a cemetery?) in order to make it seem like midnight is further away than it really is.
I also seem to remember my aunt telling me that this movie is part of a set or series, and that she had also seen others (with the lady of light and cat lady of darkness, supposedly).