I agree that you could do with more litter boxes for that many cats, but if it's just short-term maybe you should leave the hood off. I found that my cat was a bit anxious about using the new hooded litter tray first when I got it, and even now I have to keep the flap off the door (she won't push through it). There are several advantages to this. There will be more space for the cats to use different areas of the box if there's no hood. You can keep an eye on it more and remove dirty areas regularly during the day - especially if you have clumping litter. Also, the kittens might learn from watching the older cats.