If they will let you calmly hold them then get them to walk around in a shallow warm water bath to soften the balls. We used to put some in the bath and fill it a little with a rubber mat, now I use trays and they paddle around drinking the water lol. It may take a few days, and a few goes, not all at once and be careful as the last bits may have skin attached,so may be better to get the worst off and then let them rest a while and their feet dry out thoroughly.