Is it permissible to delay Sunnah prayers, such as the two Rak'ahs before Dhuhr, until after Dhuhr prayer due to obsessive thoughts during prayer and ablution (Wudu'), and constant passing of wind, knowing that Dhuhr prayer is more important than Sunnah prayers?

It is better to perform the regular Sunnah prayer before its associated Fard (obligatory) prayer. It is permissible to delay it until after the Fard, even without a specific reason, because its time extends as long as the time for the Fard prayer extends. There is no harm in delaying the pre-Dhuhr Sunnah prayer and performing it after Dhuhr. It is advised to disregard intrusive thoughts (waswasah) and to pray at the preferred time.