I recall watching this series on regular Australian TV about 10 or so years ago I think on Southern Cross 10 but don't hold me to that.
From what I remember the series was sort of similar to Charmed in how the witches were family and how at least one of them was new to magic.
It was implied that these witches come from another world which I think is Asgard as at one point they discover in their basement the formation of a doorway back to this world. But they want it remained closed because they are fleeing from their father or king who is I think is either Odin or Thor. It was a recognizable Norse God name. This portal was growing these deadly weeds on it which the characters burned but after that, unknown to them, it started to leak something that looks like mercury.
One of the plots involves this other woman who gives the family a hard time and one of the witches curses her (a huge no-no). The cursed woman later on has a mental breakdown seeing bugs crawl out of her skin and when she is hospitalized she starts choking on what looks like a bramble which one of the witches tried to steal from the doctor.
Another plot point involved who I think is the least experienced witch seeing this creature with what looked to be tentacles in the park at night. Later the other witches learn that the creature is a plant and it's chosen the least experienced witch to be its mate and it had charmed her so she wasn't meeting it of her own will.