As long as the urine was dry and you washed it or washed it and your slipper, this is pure and enough.

My brother doesn’t use the toilet properly and urinates on the toilet seat and on the floor also. I make sure to wash the floor on where there is urine but my doubt is will the sole of my slippers become Najis? I leave the slippers on the bathroom mat and sometimes the slippers are left inside so everyone climbs on the mat to wear the slippers so is the mat also impure?