Thanks for all your reactions!
In my experience brother uses a rubbing movement, but of
course there are a lot of variations. I have changed the
brother I wrote (see attachment). Is that better?
And I agree that the finger in sister is less bent, so I
added Stefans version too. Thanks by the way for that
website (BritishSignLanguage.com), I had never seen it
PS for any Spain fans who happen to read this message:
well done :)