Hello I saw your post and had to reply. I am the proud owner of 2 whippet's, both boys and also littermates. At first we only had one, Whisper , who was 9 weeks old. After a few weeks I phoned to breeder to inform her he was getting on ok, she informed me that she still had the smallest puppy left and he was about ready to go. So we fetched him 2 days later.
They are not a bit of bother. Because they have completely different personalities they get on fine, obviously they play fight. As long as you have a hubby or someone to help I think you'll find two ok. It might work better with whippets as they are fairly laid back and easy to train and you don't feel so guilty when you go out without them! whisper and josh are now 6 mths old and it has worked out fine, apart from loads of doggie poos to pick up in the garden!
Whisper and Josh are now 6 mths old and we've had so much fun with them.
Good luck with whatever you decide to do.

I've had sibling bitches without any problems either. But I had them until 3 years old and they grew up without any problems together. I probably wouldn't do it again for various reasons including focusing attention/training on one and being more doggy orientated than towards people.

I do find it difficult to understand how you can recommend this partnership as to be just "fine" when your own puppies are only 6 months old They haven't matured and they are still at the easy going growth stage.

I'm not saying that there will be trouble, but if there is, it will likely be during 8-20 months old when both dogs come into their full young adulthood. They will attempt to determine the exact dominant/subordinant in the relationship. Just natural. Since they are the same age and rank, it could be difficult for them to establish the ranking.

It will be interesting to see if you have the same opinions in a couple of years and once everything has settled down into regular placement.
good luck and enjoy your beautiful puppies :)
toodles