I am a seasoned and practised mouse-killer. perhaps I can give some advice.
Our house is built on old farm land and we did have a mouse problem at one time. They were getting in through the garage and under the connecting door to the living area.
I put out mouse poison -green pellets in trays, but I had to kill the mice myself once they came to eat the stuff.
This is how you do it: You need a couch with a gap under it, not one where the base is flat on the floor. This offers the mouse cover while they nibble. Place your bait tray against the wall.
Imagine yourself kneeling facing the couch and putting a broom handle under it, sweeping the handle from side to side along the floor without hitting the bait tray. This is the principle used for killing the mice.
Lay the broom handle under the couch to one side of the bait tray and pull the far end back a little bit from the wall so that if it was swept across it wouldn't hit the mouse bait.
Leave the broom handle there until a mouse comes a-nibbling, then sweep it across as suddenly as you can (kick it if necessary). It will collect the mouse and fling it against the nearest wall killing it instantly. Mice are very fragile. This is a far quicker and humane way to kill mice than poison, which is effective but slow and painful.
I have also used the modern mouse traps, the grey plastic ones, which are effective too. They snap shut over the mouse covering its body (nearly) and if you want, you can just chuck the whole lot out and replace with a new trap, though that's the expensive way. I re-used them.
They look a bit like this, and the best bait is a little blob of peanut butter.
