ILR after Tier2(G) for dependants: over 18 and under 5

[fdl]

Hi!

I am under Tier2(G) since 08/2013 together with my wife and one son, who was 15 years old then.
The second son was born here in 2014. We are going to apply for ILR in PEO in August this year.

1) The older son is still considered as my dependant, however, since he is over 18 now, he must fill his own SET(O) form, am I right?
2) In this form he will be considered as the main applicant, right?
3) He is living with us and has a part-time hourly-paid job in a restaurant. The money he owns from his job is not, 'fortunately', enough to have an 'independent life'. What is the proper way to fill the sections 5.3--5.7 of the SET(O) form for him?
4) It seems that he can't be considered as a part of my 'family group' for applying in person in PEO. Can we still apply somehow together/simultaneously/at the same day?
5) I am aware that the younger son is eligible for citizenship after me or my wife gets the ILR. If, for some reasons, we don't want this, is he eligible to apply for ILR in 08/2018 when will not be 5 years old yet? (His current BRP is valid until 03/2019, he will be five in 05/2019.)

Thanks in advance.

[vinny]

1) Yes.
2) Yes.
3) Truthfully.
4) Don't know. Perhaps book sequentially and see the same caseworker?
5) Yes, under to 319J or under A277, A280(b), 304-309.