Over 18 dependents

Hi,
My children are over the age of 18 (20 and 19 respectively) and we are applying for ILR. We entered the UK together in 2016 and i was wondering how the separate applications work (came on a Tier 2 general in 2016 and children are still PBS dependents).
1.) I understand they have to fill out a separate set O form which is different to mine and my spouses. Would they fill this out at the same time or after i have filled out my own form?
1b) I cannot find my own home office refrence numbers. Are these essential or can i leave these blank?
2.) They go to university away from home but due to covid they have been living at home so should they choose the "living with family" option instead of a different address?
3.) Does their driving license (as a supporting document) have to only be a month old or can they use a slightly older one (they are valid for 10 years)?
Thanks,
Hauyan

1) As far as I know they do not need separate forms. They can all be included in the same application. They simply need to pass LIUK and English test too.
1a) No need for that
2) Yes
3) No such requirement