Weight is not the whole story. Their weight checks tell you that they are eating enough hay but it doesnt tell you whether they are healthy size for themselves. A weight which is healthy for one piggy could be under or overweight for another.
My two boys, in their prime weighed, 1.3 and 1.5kg and each had a good heft which meant they were both fine.
To check what is healthy for your piggies you need to check their heft - piggy BMI - by feeling around their ribs. If you can feel their ribs with a thin covering of fat, then they are fine. If you cannot feel the ribs at all then they may be overweight.
The guide below explains.
Weight - Monitoring and Management