Enquiry about fees for 18 years old dependent child

[karthikaLaxmi]

Hi I am eligible to apply for a ILR in Nov.I have been in Tier 1.My two children aged 20 and 15yrs now,joined me at UK when they were 16 and 11 yrs respectively. I need to know the following

1. should I fill both dependent details in my form or separate one for my older child?what fees should I fill in my form and in 18 yrs old child'd form.

2. What fees should i pay for me and two children)one child above 18 yrs and other one 15 yrs) if I am going through premium service