Indeed I do. =D
Out of my rats, alot of them were brought home with their sibling.
Otto & Venny are brothers.
Garber & Akio are from the same parents.
And Sid, Ophelia, & Pocky are from the same parents.

I met Don's sibling, and interacted with him/her alot when the two were young and not ready to be brought home, but since the other little bugger went to his/her home, I haven't seen him.

We owned Frisk's brother for a week or two, but he went back to the breeder to find a more suitable home(at the time, our home wasn't ready for two dogs).