ILR Questions

I have following questions (Tier 2(Gen) with 3 pbs dependents, spouse + 16yr + 18yr old)
Date of entry UK = 19/09/2010 Date of Ext in 06/2013 valid till 24/08/2016

1. How many cohabitation letters over the last 2 years are required for me and spouse, plus time frames ?

2. Are these the correct documents for 16 yr old, any 2 of following : bank statement, credit card bill, driving licence, NHS registration document and a letter from their current school, college or university, on headed paper and issued by an authorised official of that organisation.

3. Are the above documents valid for 18 year old aswell. He has not started University and is living with parents and will finish A levels in 06/2015. He will clear LIUKT and English language test.

4. Absence letter required from employer is it just for the period absent from UK or any other absences aswell? I have (11 +11) = 22 absences from UK in total during 5 yrs approx. All are from paid annual leaves.

5. What is the earliest date we can apply for ILR.

6. We will apply by post, (me + spouse +16yr old on SET (0)) as my son is 18yr can his application on seperate SET (0) be sent by post on the same day as ours?

Please reply.

Anyone ?