I can text my sister-in-law on an Android phone from my iPhone 5 with Messages with no problem. I can text my brother, also with an iPhone 5, with Messages, from my iPhone 5. However, I cannot text both of these people at the same time. Why?
I know you can't do it. My question should have been, "Why can't Messages identify each recipient's equipment and route a copy of the message to each of them by the methods used when I sent separate texts?" Would that be that difficult to program?