Niger thistle should not grow in your yard. GF thistle comes from overseas, and is not supposed to grow here.

I buy bags specifically labeled Niger seed and it does not grow under my feeder. I don't think anyone is allowed to sell thistle seed any more, it's such a destructive invasive plant. Years ago I had a bag of some finch food and thistle did grow all over the place, but I think I've finally managed to kill it all. You can buy a finch mix, that has some Niger seed along with other little seeds that finches like.

Yes, nyjer seed is not even related to thistle...the nick name is a total misnomer. It is also infertile and will not create a whole bunch of seedlings under the feeders. True thistle is not sold as bird seed, ever.

Your thistle problem is coming from some 'real' thistle plants.

My goldfinches love sunflower seeds. In fact, this spring they crowded out the titmice at the feeder which they emptied over and over. Goldfinches have moved on and titmice are back.