Some common themes include the idea of unity. Jacob and Bella finally becoming one in a more profound way on their wedding night. The theme of acceptance is also there, as they accept each other completely, with all their flaws and differences. Additionally, there can be a theme of transformation. Not just in the sense of Bella's transformation in the original story, but also in how their relationship is transformed into a more mature and committed one on this special night.
One common theme is the exploration of their new relationship. Since they have a complex history, the wedding night can be a time to fully embrace their love. Another theme could be the blending of their two different worlds, the werewolf and the vampire - adjacent. Also, the idea of new beginnings and a fresh start in their relationship is often explored.
In many fanfictions, a common theme is the celebration of their love. Their wedding night is shown as a time to let go of all the past troubles and just focus on each other. There might also be themes related to family and how their union affects those around them. For instance, how Jacob's werewolf pack and Bella's vampire friends react to their new status as a married couple. And of course, the theme of passion and intimacy is also prevalent, but it's often portrayed in a more romantic and emotional way rather than just physical.