I'll give the writers credit where it's due - it takes real skill to completely suck the drama out of a storyline where Sonny dies then comes back and finds out that Jason and Carly are married... but man, they did it. There's absolutely nothing to see here.
I still can't believe that they just had Sonny casually stroll into the bedroom at the beginning of the episode on a Tuesday. WTF. There should've been a huge Friday cliffhanger with him crashing the wedding, then on Monday we'd have all the people close to Sonny trying to process him being alive, and have Sonny wondering why Jason and Carly are getting married. But no... Sonny's return apparently doesn't even warrant a cliffhanger on any day of the week. Nor does it warrant a big event. He really just strolled into the bedroom like he just got back from the grocery store. I mean at least have him catch Jarly f-cking! My god. Where's the drama?! This should be such a huge storyline and they are messing up literally every aspect of it. I'm not even particularly a fan of these characters and I'm appalled by how this story is being written.
She wouldn't need an annulment. The marriage is invalid since she's married to Sonny. I guess she could be conflicted on whether or not to divorce Sonny but since nothing happened except a few kisses between her and Jason I don't anticipate that. Unless the show goes all out and does a Roman/Marlena/John style affair like mentioned above and I just don't think they will or even the chemistry is there.