Stand your ground.
I would tell my girls they had until such and such a day to clean their rooms and the bathroom. If it wasn't cleaned by that day, in I went with the black trash bags. EVERYTHING and I mean EVERYTHING that was on the floor or where it didn't belong went into the bag. Out it went...yes, I stored it where they couldn't find it for a while, but they did watch me toss it in the trash bin.
Needless to say, I never had to tell them again. All I had to do was walk thru the house with a black trash bag and those 2 would go diving for their rooms.
Courtney now, slips once in a while, but the black trash bag STILL works! She sees me headed to the hallway and up she jumps. lol
Sometimes I do it just to see how fast she can move, then I head to my room and chuckle .... yes, I'm a mean mom lol