L.R.
Yep, you can't wash feather pillows that I know of. Did they have labels saying they were machine washable?
I would bet that the feathers deep in the pillow did not ever dry thoroughly and now are mildewed. You're just not going to get rid of that with vinegar (or my other big favorite, baking soda).
If you love the covers, I would cut them open, throw out all the feathers, get the covers properly cleaned (that might mean dry cleaning) and re-stuff them with foam or something else. If you're good a sewing, see if you can make them into removable covers by putting zippers in them so you can clean them.
If you're convinced there's no mildew or mold you could try spreading dry baking soda on them and leaving them to sit in the sun, then vacuuming out all the baking soda. But I suspect they're moldy in the center and the feathers are not going to lose that smell.