Adam knew what he was doing, he discussed the plan with Osana many times, as well as with Franz and Rosalind, so he wasn't afraid he'd get in serious trouble for showing up at the wedding.
Of course, the issue was not the plan, but the fact that he used The Rule of Power, and knew that he was doing everything according to the ancient law.
It didn't save him from Mariel, Zarot, and the others trying to kill him, but thanks to Gladius, no one else thought about fighting. As long as he was here, no one had a chance to even scratch Adam.
Well, despite that, there was someone who tried to kill Adam even at the cost of life.
Strangely enough, Istrid was the one who didn't want to come here and looked the most bored and uninterested among all the guests.
However, when it came to some random Phantom ruining her brother's wedding and insulting her entire family, Istrid changed completely.