Okay, I have 2 brothers. One is a lot older, so he was practically out of the house before I knew what jacking off was. My other brother is my twin. We are very close, but have never jacked off together. On the other hand- being twins and curious, we have compared every body part including dicks, but you need another option on question 2 because neither of us were erect when we did it.
We did go through a phase were us and a brother and sister down the street all played around together (playing doctor and I dare) that experimental phase we all go through. But jacking off together never happened.
Hope this helps!