My modi twins are 15 wks. At birth they were 4lb 11 (t1) and 5lb 10(t2) and have been combination fed since. On average I'd say they have very similar amounts of milk and good appetites. T1 however is gradually falling behind t2and there is roughly a 2lb difference now. Is this normal for twins? Not sure if it makes any difference but t2 pees for England.