sudden death in cats

A fellow rescuer, who is also a friend of mine recently moved into a new home. She has several cats right now whom are all supposed to be in good health and get regular checkups.
Two of them suddenly died the other day. She and the Vet are not sure of what yet. The signs look like rat poisoning but the clotting wasnt as bad as it should have been.
They had 2 seizures before they just flopped over and died. Just an hour before they were playing and eating just fine and no other symptoms before this.
She has the rest of the cats in 1 room right now, trying to figure out what to do, as she doesnt want the others to fall ill and die.
The vet is running a pathology/necropsy on the two deceased cats, but so far no real clues as to what may have happened. We were perhaps thinking Acute Anemia.
Im trying the best I can with suggestions to her but otherwise pretty much clueless right now.
Does anyone have any suggestions? Anyone had something similar happen?

There may have been a rodent that got in after injesting poisin. If the cats ate it that may be the problem. Check for any holes that a rodent might be able to squeeze through and stuff it with steel wool. this way they won't chew back through.

Please keep us posted.