Yes! Brother and sister.
We are so glad we got two together - the breeder was too! She was so happy we were keeping two of them together!
Absolutely....it's the best, if you can do it. And so much more fun for you.
I have had litter mates three times over the years. My current two were born on the same day at the same breeder and brought up as one big litter, but are not actually related! They are wonderful together.
Do you find the darker Siamese to have the stronger personality? In my experience the lighter pointed cats tend to be less rambunctious. However, I had a little lilac boy once whose personality was absolutely enormous.
That gizmo you have bought for your two is very impressive...cat heaven!