there are two options for the first part:
1.All the family members get together having family reunion dinner and watching CCTV Spring Festival Gala
2.All the family members get together to have family reunion dinner and watch CCTV Spring Festival Gala.
With the attribute clause,I am not sure which one you want to modify - all family members get together or the CCTV show.
I think our tradition is for all the family members to get together no matter there is a TV show or not.
If you want to say the TV show is a tradition,"is" is correct.