Adopting a sibling of your current dog?

I don't have littermates but Rose and Summer are half sisters (same mom). Beau and Rose are half siblings (same sire). Rose and Summer lived together for about a half year prior to us getting them. Beau and Summer were three months apart, Summer was the breeder's keeper puppy from the older litter so she was a puppy at the breeder's at the same time Beau was a puppy and they played all the time.

Confused yet?

Anyways, they all get along but no more than the other dogs do. Summer tends to favor Rose and goes berserk when we see her and licks her all over the face. Introducing Beau and Summer after 4 years of being apart didn't go so well as Summer kept attacking Beau and Beau was trying to hump her constantly. They weren't siblings but were raised as pups in the same house. I definitely don't think Summer remembered him.

We've had Beau since 11 weeks (he's 8)
Then we got Rose at age 2 (she's 6 or 7 now, can't remember)
Then we got Summer at nearly 4 (she's 8)

I adoped Gem, and a few months later a dog I believe to be her sister turned up at the shelter, I adopted her as well. upon first meeting at the shelter they were a little snarly with eachother, but once they met at home, they LOVED each other and have been extremly close ever since. my boss also adopted the brother of her dog, she had the one from a young puppy, and at a year old the brother turned up at the shelter..again not "for certain" but same age, same mix, look and act the same..they too took to one another right off the bat, in fact they were seeking each other out before they ever offically met,and they remain very close.