How old are they? Are they big-boned? small-boned? Are they healthy? Do they feel skinny? or fat?
A lot of things go into ideal weight, so it's impossible to say without knowing more about your guinea pigs. If your heaviest is 880 grams, they're almost certainly not overweight, though I guess that's possible if she's really small-boned.
I wouldn't worry about it. I'd feed them as much as they want, as long as the thing they get the most of is hay, and the least is pellets and fruit. If they get too heavy, you can always cut back.