It really depends on how calm the dogs are and how calm the rats are. Also, if rats haven't grown up around dogs, introducing will probably be harder than if they did. I've never had a bunny so I'll let someone else answer about them getting along, but I wouldn't put them together, even if I was supervising.

You don't have to get the males fixed if they're getting along (drawing blood while play fighting can be a sign of a problem, but rats play fight all the time so don't think they aren't getting along. You might also have to get one fixed if there's a health issue. But generally, no they don't need to be neutered.

There is a list of foods that are good, sort of okay, and bad for rats. http://www.ratforum.com/index.php/topic,3079.0.html Rats live best on a low calorie, low fat diet. So feeding them people foods (like pizza, ramen noodles, bad foods) really isn't the best either. Generally, if it's good for you, it's good for the rats.

For the carpet, if you set up a specific play area for them, you can put down a fleece blanket which soaks up liquids really well. If you're going to let them run all around, you might get some pee stains, especially if it's lighter carpet, but since they have a whole room to go, it probably won't smell. The smaller the area, the more it will smell, unless it's cleaned properly.

Also, you mentioned you have a cat, and it sounds like you'd let the rats run around with the bunny, dog, and cat out. That could be a big problem. For obvious reasons, haha. It might be better to give the rats their own play pen, and put the blanket down for them.

 

The rats are brothers, and theyve been together their whole lives, so they get along well.

I wouldnt have all the animals free roaming together lol. The cat stays in the bedroom all the time. The dog is really hyper, she's only like 10 months old. I dont trust her with my bunny, much less the rats. If she was with them, it would be completely supervised. I was mostly curious about the bunny, cause he is in the basement, and thats where the rats would be too.

I have a bunch of NIC panels left from my bunny's pen, so it would be easy to make a pen for the rats with that.

 

I don't believe that rabbits get along too well with other small animals. If they feel threatened, startled, cranky, or even playful, they can kick, and rabbits have a powerful kick. I know you aren't supposed to have them around animals the size of guinea pigs so rats and rabbits probably shouldn't play together.