Honestly, a lot of the other poisons aren't much safer. They affect the blood instead, preventing clotting so the poisoned animal bleeds out internally. It's more curable, but it's a long, slow death, the cause of which can be difficult to pinpoint.
Unless no other options work, go with traps instead of poisons. Not sticky traps, either, those trap all kinds of small animals (including beneficial lizards) and they all die slow deaths of dehydration and panic. You want good-quality snap traps, those break the spine and cause a quick, if not instant, death. They also have a much lower chance of killing other animals and injuring your pets.
For best effect, put the traps up against a wall. Rodents run along the edges of walls for cover, so placing a trap lengthwise against a wall will send the rat right into it. Peanut butter is a much better lure than cheese. Rodents love it.
Also, if anyone has a single rodent in their house that they want to remove alive, there are designs online for live-catch mouse traps.
Do you know where the other 4 cats are ? How they are doing ?
