I was waiting for somebody to unrecommend the ACD. Actually they make great companions for the elderly who can give them not more than a free run in the backyard once or twice a day for exercise, a mile would work. They tend to be on the fat side if not fed according to their exercise. The thing that they need in order to keep from being destructive is constant companionship. Perhaps this is not the right breed for your brother but maybe it is. This is a one-person dog that is going to be right on your heels all day. They need games such as hide-and-seek and if you are gone something like hiding some treats for them is great stimulation. They also need lots of socialization from the start because they are a one-person dog, but I think you would have no problem with that since you live with other people and animals already.
Anyway the others are right in saying that any dog can become protective of their owner. Autumn is a friendly toller but will protect me without question if she needs. She's even trained to be on the guard when we go for walks in the evening, I use "place" for a command to point out any people (we walk in some dark places and I can't often see so she will point at people like a pointer until I say ok) and "guard" to let her know that I want her to act tough. If she feels somebody (usually mean looking men coming from the bars) is too close she will growl and I usually cross the street, and if they get really close she really starts to snarl and bark (while still at heel next to me), but she would never bite without my permission. I thought of doing classes for protection, but I guess she doesn't need it. I think whatever breed you choose will work out just fine since you seem to be a responsible person who is willing to ask and to take advice from others on raising a dog.