In my mind, Sam and Daniel are just as close as they are in canon, but it doesn't actually read that way, I know--I've neglected that friendship quite a bit in comparison to Jack and Teal'c's, which, you're right, are rather different. I'll try to amend the dearth of Sam in the future, though :)
And my approximate ages for the Abydon kids as of "right now" in the story would be: Daniel=16, Skaara=21/22, Sha'uri=26/27. Sha'uri's age is based on the age of the actress from the movie; Skaara's a little younger than his actor, just because he supposedly reminded canon!Jack of his son, and I figure any older than late teens at the time of the canon movie was kind of pushing that. So Sha'uri's old enough that she might've watched over Daniel when he was a kid.
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And my approximate ages for the Abydon kids as of "right now" in the story would be: Daniel=16, Skaara=21/22, Sha'uri=26/27. Sha'uri's age is based on the age of the actress from the movie; Skaara's a little younger than his actor, just because he supposedly reminded canon!Jack of his son, and I figure any older than late teens at the time of the canon movie was kind of pushing that. So Sha'uri's old enough that she might've watched over Daniel when he was a kid.