Your ( stippling foot) should ( hop) as in, it is above the fabric sandwich while idle, and goes up & down while stitching. So, it is probably right.
Are the feet you purchased Viking feet? Or are they some ( generic) set?
I'm not sure what you mean about the duel feed foot not being ( interchangeable) my duel feed foot works with the feed dogs, evenly advancing the fabric top and bottom. It is different from a walking foot which { takes steps} as you sew.