Soaking really does nothing to stop bleeding. It needs agitation to release the loose dyes. If you don't want to spring for Retayne, get some Color Catchers at the grocery store and hand wash, don't soak, the FQs that are bleeding.
Swish them around in the water with the CC until the water turns colored. Change the water and do it again. When the CC is dark, change to a new one. When both the water and the CC are clean, you're done. If that never happens with a FQ, I wouldn't use it.
You can save a lot of time by doing color batches. No real need to do 56 single FQs cuz if one doesn't stop bleeding, it's easy enough to isolate.
Retayne is a huge amount of work for 56 fat quarters because of the temperature required (140ºF), the constant agitation necessary, and the multiple colors and size of the fabrics. Odds are great that the problems is excess dye, not unset dye.