Funny prank to play on skype?

Okay so my brother skypes his friend most days and they play minecraft. I'm friends with the sister of the guy my brother skypes. Any ideas I could play (get the sister in on the joke with me) over their skype calls? Lol.

Pretend you are smart.

Here are some things you could do if you're in different houses:

- you could both constantly call them as an interruption.
- you could shut down the internet for one or both of them.
- ask them for the computer, using an excuse like, 'i need to copy something onto my usb, can you go outside', and ruin their minecraft game (for e.g kill them both, or ruin whatever they're doing)