Unfortunately there is no super easy way in the GUI to bulk edit those volume thresholds. If you use the manage nodes screen you can check the boxes for them all and set the thresholds for more than one at a time, but you still have to do a lot of clicking around and there is no search for volumes button.
For things where the GUI fails me and there is no API command then the only place left to go is direct database changes
insert into [ForecastCapacitySettings] (InstanceId, MetricId, Enabled, UsePeakValues, WarningThreshold, CriticalThreshold)
select distinct volumeid, 3, 1, 0, 80, 98 from Volumes
where caption like 'c:%' -- figure out how to define a where condition that includes only the disks you want to make this change to, since you mentioned the nodes are in a group you could join volumes to nodes to containermembersnapshots to tie these together