As to Sam's mother dying, I've heard that her mother died when she was 12, but I've never tracked down whether that was canon or fanon.

As to Charlie, he looked to be an age-mate of my eldest, who was born in March of 1985, so I've always taken 1985 to be his birthdate. You could certainly make a case for his being born in 1986 and being big for his age too, since neither of his parents are short. I don't think that canon offers anything that would tie the birthdate down firmly.

By now you've probably made your decisions as to what the time line is, since I was away for the weekend and didn't see this until now. But for what it's worth, those are my two cents.