I would agree, those stones look like they could be easily swallowed.
I would try and remove them ASAP then leave your tank bare bottomed for a good couple of weeks and see if your Axies pass anything.
If you can get an over head shot and/or a belly shot that may help with the question of gravid versus chubby, it i difficult to tell from the current angle although they don't look especially chunky from what I can see.