My Neighbour's Cats

There are two fat cats but I do not know which species they belong to.
In particular, a white cat.
Sometimes I find her in the living room eyeing the fish in the fish tank and I say 'No kitty, that's not your dinner'.
She will escape through the living room.
But oh boy, she is one smart Alec.
She will re-enter the house through the utility room, kitchen, passage way and re-enter the living room.
Should I encounter her at the entrance of the living room, she walks away nonchalantly as if 'tomorrow will be another day'.
I actually have to laugh at her demeanour.
Other times, she escapes when she sees me walking into the room.
Next thing I know she will be pawing at the patio door wishing to get at the fish tank.
Other times, I find her in the garden ... meow meow she says to me and in reply I say 'You are not having my fish for dinner'.
I love eating fish and usually cook for myself but the kitty has stolen many meals from my kitchen while my back was turned.
HBH reminds me to close the utility door or kitchen door before I go to bed but the tendency to forget is great as I enjoy fresh air in the house.
It's to the cats' benefits for they will ransack our dust bin for food.
I am allergic to cats; medically proven, and it irritates my nose uncontrollably, yet I cannot bring myself to be mean to the cats.
What would you do in my position?
Thanks.