Tuck is able to speak to Jack from anywhere in Jack's body - that's up to a good four or five feet from the receiver in Jack's ear. So how come Tuck can't pick up from or send to the receiver when he's in Lydia, but still within four feet?
For that matter, why was Tuck in Jack's mouth for the kiss?
Why did Jack's doctor, co-worker and boss get invited to Tuck and Lydia's wedding?
Probably because in the interim, they became Tuck and Lydia's friends too?
They needed more guests to fill out Tuck's side? Does Tuck strike you as the sort of guy that keeps close to his extended family.
So Tuck's vessel caught champagne that Jack drank, and Tuck didn't find it at all nasty or unhygienic to drink it himself? It contained Jack's saliva and bacteria!
Tuck's an alcoholic in a desperate situation. I don't think he'll have too much of a problem with that.