Better sent in a support ticket so you can get GM response, and so that you have something to show them if a problem ever comes up but..
generally, as long as the two forum accounts never touch the same IP address, you're good. But if they do, or if the other IP address has someone else voting through it, then both of you could be banned.
But I am a player .__. for something like siblings needing to vote, you need to clear that with the GMs.
Also, why would he vote and give you the credits if he plays too?