Niki Gomes

I won't write a very detailed explanation because it would take me forever Lol. But put it shortly, the Zhang family have branches. The original Zhang who was kinda royalty and the other Zhang families. The original Zhang have the same tattoo XiaoGe has and the other families have the tattoo Fo Ye has. Their tattoos are similar but represent a different mythological creature. Fo Ye actually die but he was already old and he seems to have had kids. Since the books also have some plot blanks and lots of things are left to interpretation, I believe For Ye either didn't have the longevity since his family "rebel" and left the original Zhang and not having longevity was their punishment. Or he just gave up his longevity because he found the love of his life. Although the last option is romantic I kind believe it's more likely to be the first option. But of course you can believe otherwise, since there is room for interpretation we can believe Fo Ye and XinYue are living happily ever after in a village in the mountains never growing old :)

Even though I started reading the books and trying to keep track and make sense of the events in the series, I still get frustrated with the mess they did with all the plot holes and confused scenes and casts in the series.
In TOTS Wuxie is more resourceful because the events happened when he kind "replaced" his uncle three in the Wu family organisation. He was the boss at the time and he tries everything to help solve the mysteries and finish the mission XiaoGe and Uncle Three left him. Remember in TOTS XiaoGe is behind the bronze door. At the end of the book "Ten Years After" which happens after the events in TOTS Wuxie need to make a choice ( that may be related to whether XiaoGe will come out of the bronze door or not. At least its what I understood after reading three times the same chapter Lol). This choice is something like Wuxie giving up his obsession with mysteries and stuff. Few minutes before XiaoGe comes out Fatty asked Wuxie what he and XiaoGe will do after XiaoGe comes out of the door, Wuxie says, he is retiring to live a peaceful life in a village and kind of comment that the village might be a place XiaoGe would like (this part it's open to further interpretation ?). Okay, to summarize, I think Wuxie was more resourceful in TOTS because he was the boss at the time, and in Reunion he is coming back after the retirement and he is no longer the effective boss in the Wu family organisation.

Actually not. If you follow the events in the books and not the age of the actors (this also made me confused before I started reading the books), Tomb of the Sea comes BEFORE Reunion (The Lost Tomb "3": Sound of Providence).

According to the events in the books, TOTS comes before Reunion. Maybe the screen writers made a mistake or let it a bit confusing regards the Wang Family. Who knows :(

Following the events from the books, you would have:
1. The Mystic Nine
2. The Lost Tomb
3. The Lost Tomb 2: explore with the note.
4. Ultimate Note
5. Tomb of the Sea
6. The Lost Tomb: Reunion

SPOILERS AND EXPLANATION:
Just to explain: Tomb of the Sea happened before Reunion because in TOTS the events happened during the 10 years XiaoGe was locked behind the bronze door. In TOTS you can see Wuxie and other characters talking about XiaoGe and that they're waiting for him to come back. And also they're trying to find clues that may help him with this ultimate mission.
In Reunion, XiaoGe has returned after staying ten years behind the bronze door and the events that follows in Reunion are after Wuxie had waited for him in TOTS. Then, The Lost Tomb: Reunion is the last one in chronological order.
That's according to the books written by Kennedy Xu aka Xu Lei