There is no punishment that can be conceived of by man that would bring justice in this case. Even drawing and quartering would be grossly insufficient.
These are dangerous, rabid animals and should be treated as such. Don't try to punish them. Don't try to extract justice. Just remove them from this Earth as quickly as possible.
Take them out back, shoot them, burn the remains, and bury their ashes with with equal measures of lye in a landfill somewhere.
The victim and her children (who are also victims of these animals) will spend the rest of their lives trying to recover from what was done to them. They deserve the right to do so without worrying that the animals that did this to them may get out someday and do it again.