I only have one bird so can't answer with any authority. Frankly, Timber demands as much time and attention as I can provide which is one of the reasons I haven't considered another. A lot of greys are "needy" in my experience.
However, from everything I've read on the forum and other places, the answer to your questions will be "it depends." Sometimes the birds like each other and sometimes they don't. Much like people, they are very independent about their likes and dislikes. If you get another grey, what if they decide to become mates? If that happens, they are no longer companion birds and focus on their mate instead of being bonded to you. Is that something you want to risk?
Others here have multiple birds and can answer this question with their own experience and I'm sure they will chime in. Good luck and God bless