If they are this heavy, they are coming in from outside. Get a bag of fine steel wool, and around the outside of the house, go around and EVERY place the size of a nickel or larger, stuff a bit of steel wool in there. Mice/Rats cannot chew this, and will not be able to get in. Do the same all the way up at the roof gables, mice can climb like you would not believe! Do the same under the house.
That will 'seal' the house, and allow you to trap out the remainder. Sooner or later, if small ones are geting in, a BIG one will, and trust me I know, you do NOT want that to happen
