Variation in PBS extension to ILR application

Hello members,
I have recently got my ILR visa Tier 1 (General route). now I am applying for my dependent ILR next week and needed guidance. Their status is following.

Granted Initial Entry Visa : 26-7-2013
First entry to UK on : 8 -9- 2013
Visa extension on : 27-5-2015
Applied for second extension on 26-5-2018 as existing stay was expiring on 27-5-2018.

I have following questions now.

1) Can i apply for dependent's ILR on 28-05-2018 by varying their extension application. If i understand correctly the continuous period starts from day initial visa was granted and the time from initial visa grant to first entry in UK can be counted from 180 days absence. Kindly correct me if this is wrong else dependent's application will fail.

2) I have given dependent's original passports and BRP as part of second visa application, which is already under review by Home office The SET(o) says that if I am not submitting valid passports, then i should give (a) reasons and (b) any other proof to identify their name, dob and nationality. Can i give their old expired passports?

3) Is SET(o) the correct document to be used for dependent's ILR

4) In SET (o) does the dependent needs to submit, their proof of income or that of applicant on which they are dependent upon. Their is full section on this, shall i completely ignore as dependent applicant not applying.

5) As my dependent consists of Spouse and 2 children under age of 18 years, when I am filling out SET (o) for children - will their main applicant be me or my spouse.

Appreciate group member's help in helping my dependent's visa. This would save our family both time and money as correctly getting variation application would save cost and possibly refund of extension application.

thank you
Hassan