I think Youmu is Toad, but instead of being a mushroom person exactly like Toad, she's a half-human half-mushroom in the same way that she's normally a half-human half-ghost. Her "ghost half" is the mushroom she's holding.
If that's true, that would make Yuyuko the devouring giant ghost ruler (just like she is in her normal role).
As for Marisa, I'm just throwing out an idea here, but maybe she's Gino? The star motif fits.