Well, either you failed that Will save; or there wasn't anything to save against; or Creation has some awful prejudice against using brains as group housing and won't let your headmates roll separate Will saves!

...It's almost certainly one of the first two.  Creation is very tolerant and will at most demand that you take a feat about this sort of thing, not rule against it entirely.

Well, either you failed that Will save; or there wasn't anything to save against; or Creation has some awful prejudice against using brains as group housing and won't let your headmates roll Will saves!

...It's almost certainly one of the first two.  Creation is very tolerant and will at most demand that you take a feat about this sort of thing, not rule against it entirely.