So I had twins, Xander and Xaiden. Xander doesn't show any kind of emotion and he barely cries. Xaiden smiles, plays, yells etc. They're almost 2 months. Should I be worried about anything? Xaiden is holding his head up and be flipped over onto his stomach already. Xander is way behind Xaiden. Could this be like, a delay thing or just him being lazy?