Anyway yours disks are dead (zfs point of view).
I'll suggest to remove one failed disk and replug a new one, normally zfs should resilver it.
I m more familiar with solaris version of zfs.
What about the scrub command?
Did u try replace command ?
Try a zpool status -xv mulgore for more details
Try to repair:
zpool scrub mulgore (can be long)
zpool clear mulgore
request after with zpool status
For replace :
zpool replace mulgore bad_device new_device