1, because Tet is the most important festival in Viet nam, most Vietnam return home for Tet.

2,  although they had  prepared for Tet for a week, they have not satisfied yet.

3, you 'd better visit your relatives at Tet.

4, she does not wear a company uniform because It is unnecessary

1.Tet is the most important festival in Viet nam, therefore most Vietnam return home for Tet 

   ->Because Tet is the most important festival in Viet nam, most Vietnamese return home for Tet 
2. Despite having prepared for Tet for a week, they have not satisfied yet
   ->Although they have prepared for Tet for a week, they have not satisfied yet
3. You should visit your relatives at Tet
   ->You"d better visit ....
4. It is unnecessary for her to wear a company uniform
   ->She does not need to wear a company uniform