William doesn't like this. Sure, it's nice to have friends over for dinner, but something about how last minute this was is ominous.
It could just be Edward's lack of planning, but the fact that the rest of the family went along with it without argument, the fact that Alfons and Delilah simply agreed and accepted the help of Winry and Sarah, that made him curious, and it worried him.
Clearly, Edward had something he needed to tell the family, and it wasn't good.
Dinner went by quietly, with quiet conversation, and minimum mess on Joseph's part, thank goodness.
William waits quietly for Edward to speak up as dinner is finished.