I think you should chill and let nature (and the poison) do its work.
Mice are intelligent, just as mentioned above, and they may get suspicious if you keep interrupting their habitat, so I would wait about a week before going back up in the attic, let them think you have forgotten about them.
Looks like the attic is their base of operation, so let them get back into the routine of finding food.
About the possible entry points, you definitely need to fix these ASAP, cause mice wont be the only creatures wanting to take up house with you.
I bought a house about 14 years ago that was 10 years old when I bought it.
I was watching tv one night and a mouse came down the steps and jumped behind the tv.
This freaked me out and I bought traps and poison and set them out all over the house.
I got to looking around outside for entry point and I found a perfect one.
The house is sitting on a concrete block foundation.
There is a metal door that allows access to the crawl space under the floor.
I found that the frame for the access door has the concrete blocks surrounding it.
The blocks on the bottom of the door had the holes that are in the center of the blocks totally exposed.
The mice (and spiders and snakes) could easily go under the door by dropping off into the block then coming back up on the other side.
I couldn't believe the builder left this wide open (made me wonder what else I might have missed in the construction).
Anyway I filled the holes in the blocks with a couple of bags of concrete.
I also found a hole under the downstairs tub that possibly allowed the mice to move from crawl space to my space.
It was stuffed with fiberglass insulation but that's no barrier to a real mouse.
I patched it the best I could, which wasn't the proudest job id ever done. (The space to get to it was very limited.)
Anyway, no more mice, although I still have them getting in my workshop/shed, but I did some work on it a couple weeks ago and haven't caught any new ones since.