G.W.
I have twin 7 year old boys. I wouldn't really address it at all. Let each guest decide how they want to do it. I have found that most people will buy two less expensive gifts as opposed to one more costly gift which is always fine by me. If there are an uneven amount of gifts then let them tear into it together or wait and open gifts after the party as many are doing today and handle it in private if there is any issues.