If they are healthy, those weights are fine. Do they appear to be thin or have something else wrong with them? Are they hunchy? If they seem healthy and are doing well with good appetites, it's fine!
Going by weight can be deceiving when it comes to health. Some chins are smaller than others, that's just how it goes! Some adult chins may end up being only 500 grams, some may be 1100 grams...and those weights are healthy for them.
What can end up being unhealthy is trying to get the weight up by means of giving chins supplements or treats or whatever you want to call it and just have them gain fat weight. You want for a chin's weight to level off feeding good quality pellets and hay. This is why you need to be less worried about weight and more concerned with the actual health of the chin. Muscle mass and tone is so much more important than fat, of course. If a chin is leaner and has good muscle tone and a good appetite, there should be no concerns about the gram weight.