#1/yellow wall I’d want to know the age. If it’s a yearling or maybe early 2yo who has a more mature hind end, very typical butt-high growth stage that doesn’t bother me at all. The size of the feet and slope of the pasterns suggest he’s not a yearling, though if he is, the pasterns alone would turn me off. I realize he’s weighting that LF more than the RF, but as much angle as there is, IMHO that’s too much for a yearling who should be more upright than that
#2/red curtain isn’t butt high at all if you draw a horizontal line across the peak of the wither and the peak of the croup
#3 is one I’d want to the know the age of. It may simply be a more mature-looking young horse who just hit a butt-high growth stage but the hind end doesn’t look that much more mature than the front. He’s actually just barely a smidge butt high. The illusion of more is from the dip behind his withers and the subsequent slope up to his croup which is peaked (would want more info on him, to decide whether that’s ok for now or not). It’s not remotely a sway back, just a developed wither with a drop behind it
#4/right-facing horse looks very much like #3, so even if it’s a different horse, my comments are the same
None of these backs are sway