My child’s was submitted immediately after the other parent got citizenship. I was delayed because I mysteriously lost a chunk of time with SEF/AIMA so it’s just a coincidence that it was more or less the same time.
If they have been resident on any basis (not just GV) for the required length of time, yes. BTW it looks like language and close connection are also already creeping into renewals - I’ve seen reports of people being asked to show proof that they are learning the language. If your 18 year old has done the time there is no need to be unmarried or in higher ed, or dependent in any way … they’re treated as any other adult 6.1 applicant.
100%. Also slightly different criteria at 13 and 16. For example, no criminal record required at 15 (because Portugal’s age of criminal liability is 16).