hi there,
i'm not going to say nothing is wrong with your chins cuz i dont know that, but i do know that weights will always vary, for a few reasons.. my vet has told me that before. i weigh my guys once a month, here is some of their weights:
587 - 598-587-589-581-570-564-560-574-566-583-590-574 -- his highest weight is: 635
644-687-704-680-676-671-647-657-665-665-657-633-654-640
552-641-650-668-675-687-693-668-613-630-615-630
just for a few of my chinnies... they are all healthy [knock on wood, hope i didnt just jinx myself..
] theres quite a difference from some of their highest and lowest weights.. i forget exactly how much my vet had said is normal weight change, but if it isn't super drastic, i wouldnt worry... as long as everything else is normal... eating, playing..etc..