Same Rasi and different nakshatras is acceptable, bridegroom's if comes first is more preferable. In the case of same nakshatra, if the pada of the bridegroom comes first, it is better. But, 108th pada from the bride's nakshatra pada should be avoided.
Same nakshatra in the cases of Bharani, Rohini, Ardra, Pushya, Aslesha, Magha, Hasta, Jyeshta, Moola, Purvashadha, Dhanishta,Satabhisha should be avoided.
