Size Of Tetras - Any Cause For Concern?

From the first week (2.5 months ago), two of them always appeared to be rounder than the others, one in particular, and I thought they were female with the largest one being pregnant. The two smallest I assumed were males, and the two 'in between' I was never entirely sure if male or female (but am now thinking one is female as it's developing a rounder belly).

I've never seen any eggs in the tank, however, so I'm not actually sure that any of them are pregnant.  Instead, I'm wondering if the two largest-belly ones are actually just so because they are first for food, while the 'in between sized' one (which I'd assumed may be female now) has developed its food-retrieval skills.

In the pics, you'll notice that 2 of them are much rounder-bellied than the others (and possibly that one of the remaining 4 is slightly rounder). Firstly, do you think that they look healthy enough or is their size anything to be concerned about? Behaviour, activity levels, appetite, position of resting in tank, etc, are normal, and water readings consistent and 'good'. [ie: do you think that it's simply a matter of 2 (or 3) females and 4 (or 3) males, or that the 2 rounder-bellied ones are of concern because of their size, and if so, what ought I to do about this?]  Looking at them straight on, their bellies are rounded not just depth-wise but also width-wise (as you'll see from one of the pics where the light is shining off its stomach.]

NB. There is one pic (ends in 233, if the number shows up) where one of the large fish is blurred; the other large fish, in front of the cave, is a much truer likeness of the size of each of these larger fish.

Thanks in advance for your thoughts.

Thanks, Sue. Yes, definitely no sticking out scales - had fantail goldfish in the past with that condition so would look out for/recognise that if that were the case. Re eggs, with pygmy cories in the tank as well doing a very thorough job, I think you're right - they'd be eaten almost immediately. Thanks again - good to get an objective/outside opinion.