Does anybody know if it's true that Tackey & Tsubasa are a couple?

Answer 1

I don't believe so. I think it's just a false rumor.

Check out this fan site and ask people there:

http://d-addicts.com/forum/viewtopic_15430_105.htm

Answer 2

It was just a rumor that was spread and is not true

In an interview here are some statements that make it false:

Interview with Takizawa:
Q: The turning point was when you entered Johnny's Company 4 years ago?
A: I had a wish of getting married long ago because I wanted to have my own kids. At the end of 7th grade, I wasn't doing really well in school, so I thought about things like "How about getting a job and will I get married in the future?" So, I joined Johnny's, thinking about doing one thing that no one has done before. It's not only the entertainment area, anywhere is fine for me. I admire "Hikaru Genji" when I was little, and my older sisters like Kinki Kids, so we usually go see them together.
Q: Why do you want kids so much?
A: I am the smallest among my siblings, so I want things I can protect and take care, even if it's some little puppy. I really wanted to a younger brother or sister. When I told my mom, suddenly my mom happily called "Papa~." I said, "Why are you calling Papa for?"

you can find that interview there: http://www.geocities.com/kamisen_2000/takizawa.htm