Goldfinches are in flocks at the moment, I counted 18 on 4 feeders in our orchard on Saturday, and the Cats being there dont make a dying bit of difference, although they are behind bars!! Nyger seeds are fine, but also Sunflower hearts, they love them, you will get lots of other species too, if you feed hearts. We get Blue, great, Coal, Willow Tits, Green, Gold Finches. Nuthatch, Woodpecker, Siskin etc all feeding on the hearts.
Good luck encouraging the birds they are a delight to watch and hear.
Dawn.