Ego:
I think that your question(s) might be made clearer. Maybe come up with a couple questions you have and get some responses. The sister who is three years older would have been in the age range for exploration sex games that is normal. However,
I feel like this was more exploration than anything. However I do remember when I was a few yrs older that same sister fondling me multiple times to completion.
That goes above and beyond for an 11 or 12 yr old to bring you to orgasm. (A child who is not yet able to ejaculate is still able to have an orgasm by self-stimulation or at the hands {or mouth} of another.) So, if you experienced orgasm without ejaculating at that time, it is normal.