Two at once is fun. Greyhounds are like snowflakes, no two are alike, and the different personalities are wonderful to watch evolve. When they first arrived together (into an established pack of two), Aiden was and still is such a loving, silly, boy (and smart AF) while Paddy Mayhem was loving and total mayhem (rest his soul) (and smarter than AF, lol). LadyBug and Zeke-aroni were littermates who arrived together into an established pack of three; B&B arrived together into an established pack of three (?; I forget now!); the three girls arrived together into an established pack of three. My thought is that you pretty much get what you expect and I just expect that everyone will get along and become happy campers. Of course there are some adjustments along the way [cough Paddy cough] but two together are double the fun. And the love.
Let us know what you decide!