Well it is obviously shown that Sams mom doesn't feed her(unless Sam was lying) i was thinking maybe thats the whole reason she borrows money from carly and freddie because her mom doesnt buy her clothes and food ect. but when you think about Sam has really cute clothes how could a mom who doesn't care for her buy her such nice clothes? (and by not caring for her i mean not feed her and stuff i am sure deep down sams mom loves sam-at least i hope)
as for sam and freddies dad i think either they are both dead or sams dad died and freddies left although it would be interesting so have an dramatic episode were sam/freddies father shows up out of the blue and theey are all like 'you expect me to just let you back in my life i ahven't seen you since i was 2' or somthing like that
i think carlys mom died from somthing maybe the navy or and illness or maybe even a car or plane crash