فَمَنْ كَانَتْ هِجْرَتُهُ إِلَى اللَّهِ وَرَسُولِهِ، فَهِجْرَتُهُ إِلَى اللَّهِ وَرَسُولِهِ
Whoever's migration was for Allah and His Messenger, their migration is reckoned for Allah and His Messenger.
The first مَنْ introduces a conditional construction. كَانَتْ هِجْرَتُهُ speaks of the actual purpose, while the later فَ introduces the consequence. Identical wording on both sides is not pointless repetition: the first clause identifies the intention; the second points to the religious assessment and reward associated with it.
In إِلَى دُنْيَا يُصِيبُهَا, يُصِيبُهَا means 'which he obtains.' In يَتَزَوَّجُهَا, the verb means 'whom he marries.' The attached هَا refers back to a feminine expression.