Name a movie that had Vijay and director Shankar working together

Seetha, the movie directed by S.A.Chandrasekar had his assistant director Shankar and son Vijay doing small roles.

P.S : They have probably worked together for more than one movie. Vijay has been child artiste for several S.A.Chandrasekar movies that could have been having Shankar as assistant director. No documented facts available to substantiate.

Can you relate the 80s' movie 'Thaayam Onnu' with any of the recent releases?

Naan Avan Illai. Thaayam Onnu is the last film that had 5 heriones for the hero. Starring Arjun as hero, it had Nirosha, Shanthipriya, Pallavi, Rekha and Madhuri as heriones.
Naan Avan Illai with Jeevan as hero has Sneha, Namitha, Jyothirmayi, Keerthi Chawla and Malavika as heroines.

What were the earliest instances of Kamal Haasan (then, Kamalahasan) being involved in the writing of a film.

1. Unarchigal (1976) -- He co-wrote this film with R. C. Sakthi, the director of the film. He also rewrote the film for its Malayalam version.

2. Meendum Kokila (1981) -- The story is credited to Hasan Brothers (Kamalahasan and Chandrahasan) -- Ananthu wrote the screenplay (incl. dialogue). In a way, this served as a precursor to their first home production (Hasan Brothers), Raaja Paarvai -- written by Kamalahasan -- that came later in the same year.
[Bonus trivia: The title, by the by, is a take-off on Balu Mahendra's maiden film Kokila (1977; Kannada), which starred Shobha and Kamalahasan.]

What's the registration number of the container with the stolen money in Thiruda Thiruda? And, what is it a reference to?

SKF 1138.

This is, probably, a reference to George Lucas's sci-fi film THX 1138. (Courtesy: Wikipedia.)

What's common to Maniratnam, Kathir and Karu.Pazhaniappan?

Their tamil debut movies were produced by Satyajothi Films.

Trivia courtesy: Kamaraj C.

Name the director to have directed most number of sister pairs.

Maniratnam.

Ambika, Radha (both in Idhayakoil)
Radhika (Pagal Nilavu), Nirosha (Agni Natchathiram)
Banupriya (Thalapathi). Shanthipriya (Anjali)
Shalini (Alaipayuthey), Shamli (Anjali)

Trivia courtesy: Kamaraj C.

Connect Kiran's role in Anbe Sivam and Bhumika's role in Sillunu oru Kadhal.

Both of them have been dubbed by professional singers. While the former was dubbed by Anuradha Sriram, the later dubbed by Chinmayee.

Trivia courtesy: Kamaraj C.

Harris Jayaraj's relative is also a famous music director in tamil. Who is he?

D.Imman (Actually, he is Immanuel).

Trivia courtesy: Kamaraj C.

The audio release which movie had a couple of Donkeys as chief guests?

Ennai Paar Yogam Varum

where is the title "nee naan nila" borrowed from?

This is the title of a novel that I read 15 years back.

I am still trying to recollect the author. readers from help!!

S.Ve.Sekar's son Ashvin is making his debut in a movie. connect this movie to Kandukondein kandukondein.

The movie is called "Vaegam" (speed)

If you remember, this is the 'unlucky' title of the movie that Ajit tries to direct in Kandukondein Kandukondein

The tagline of "unnale Unnale" is based on which best seller?

"Men are from Mars. Women are from Venus" by John Gray.

Which Hollywood blockbuster has been released in Tamil as Paruthi Veerargal?

300

Which film is using the Bob Woolmer murder to promote their story?

Lee. The posters draw a parallel between Bob Woolmer's murder & coach Prakash Raj's murder in the flick.