Japanese beetles are relatively harmless to humans but they are known to wreak havoc upon lawns and gardens and are not something you want in your house. To get rid of Japanese beetles in your house, the best method is to spray pesticides in all the places that you have seen them and especially on the corners and edges and entryways into the home. There are also Japanese beetle traps that work to attract the adult beetles.
Begin getting rid of japanese beetles in your house by sweeping them up and flushing or vacuuming them. Then clean all areas thoroughly and seal cracks and crevices that you may see they are coming in through. Limiting their access and keeping areas clean will be your best defense.