@HikaruIII - Maya and Naoto were raised in the same orphanage (Lamb Garden), and so even though they are not related by blood, they were almost like brother and sister. Naoto protected Maya from some bullies, and since then she's adored Naoto. Later on, Naoto saved Noel's life in a fire, which resulted in his adoption by Noel's parents. Hence, he is not related by blood to Noel, but Noel sees him as his older brother . . . and didn't know he wasn't until very recently. In fact, Noel's parents wouldn't mind seeing Noel and Naoto married.
All the above information may be discovered by re-reading the series.