Poisoning:
 
Carol, the symptoms would depend on the poison.
 
Have full necropsies with toxicology and pathology done on those who have
died.
 
Have your vet hire the vets at the ASPCA Poison Control Center to
consult.  the price is per CASE, so your vet can get a lot of help for
a reasonable cost.
 
http://www.napcc.aspca.org/ ASPCA National Poison Control Center
http://www.aspca.org/site/PageServer?pagename=apcc
(alternative link to above site)
 
A few snippets from three places on their site:
>The ASPCA Animal Poison Control Center is the premier animal-oriented
>poison control center in North America.  So it's the best resource for
>any animal poison-related emergency, 24 hours a day, 365 days a year.
>
>Make the call that can make all the difference: (888) 426-4435.
and
>The ASPCA Animal Poison Control Center has specially trained veterinary
>toxicologists on-duty around the clock.  They have available an
>extensive collection of scientific journals and books as well as
>sophisticated databases available nowhere else.  The center's clinical
>experiences from the past 10 years can be rapidly reviewed for
>diagnostic and treatment insight.
   and
>Our staff veterinarians have a wide range of information specific to
>animal poisoning.  They also have an extensive collection of individual
>cases -- more than 600,000 -- involving pesticide, drug, plant, metal
>and other exposures in food-producing and companion animals.  The Center
>has extensive experience in assisting veterinarians in poison management
>by providing immediate and specific treatment recommendations.
 
They also can help individual owners but in something this serious, with
several ill in hospital have them work directly with your vet by having
your vet call for optimal effectiveness.
[Posted in FML issue 4654]