Seperate or not?

I bought 3 female Russian winter whites last year which were all living together in one cage. After a couple of months, one of them was being bullied and had an injury on her belly where the gland is, so I seperated that on from the group to live on her own. Now, months on, the other two keep sqabbling and sqeaking at each other which looks to me like they try to clean each other or push themselves underneath the other one. A few times, the squeaking is very loud like they are in a proper fight but they are always pulled away from each other straight away and there are no injuries to either hamster.

Also, one seems a lot fatter than the other. The fatter one always takes more food and sometimes sits in the dish so the other can't get any food, but, the smaller one always seems to take over the wheel and pushes the other off. I tried putting two wheels in but it doesn't make any difference.

My question is, do they need to be seperated?

[souffle]

Personally I would say separate them now. It appears that the dominant hamster is hogging the food bowl and the other is not eating enough. She is also losing weight and condition due to the stress of being bullied. It is better not to wait till you have blood drawn.
With dwarfs you should never have a food bowl in the cage unless they are alone. There is always one who takes it as their territory and will not let the others feed. You should remove it and scatter feed them. Hide food in corners and in the litter. The bully can't be everywhere at once so the other hammie has more of a chance to get some food. If you think the smaller one is becoming reclusive and hiding away a lot she is not having a good life really is she and is quite depressed and miserable. The high pitched screaming is not a good sign and nearly always results in injury in the end when one snaps and attacks. It happens all the time and I would say very few dwarfs last any time together especially as their hormones kick in and they mature. You will feel a lot better if you know there will not be a bloodbath one morning and you will find the hammies become much more tame and friendly.