Because they all grow differently, it's really hard to compare one to others. As long as they continue to gain things are going good. If they lose a small amount and then puts it right back on, things are good. If they lose and continue then you have something to worry about. When weighing, try to do it the same time of day and routine l each time.
Most, if not all of my leopard hatchlings have passed 50 grams by 2 or 3 month old. So those weights sound ok. I agree with the above. Steady gain at their own rate.