Sexing gerbils one month old, please help!

[hesperidainblue]

Last year I bought what I thought are two females. But smaller gerbil was a male.
They did not bread for weary long time (till they were 5,6 months old), and last two months they started, first liter all pups died.
Next month second liter all survived healthy and playful. 
General plan was to when pups age one month to separate female and male and to give them as company 2 pups.
Liter was of 4.
Just after labor (15 August) they wanted to bread so I have removed father but she was so stressed without him so I have put him back after 5 days, when heat period was gone, because he become depressed alone (I used split cage but with glass) and mother gerbil dig so much that she hurt nose and I felt sorry to keep them apart.

But this day exactly month after pups were born. They wanted to mate. I have separated them right away.
I have had another big aquarium ready for that (no more split cage) just I was feeling bad to separate pups till now.

Pups left with mother are fine they sleep together, but father is not weary pleased with pups he got he doesnt show them much attention as he was when they all were together...

I do not have names for them yet since I am weary hard to tell them apart and I do not know they gender.

First one no1 is one of playful hard to handle as his cosine no2 with same head stripe they are smaller slightly then no3 and no4

Here are images no1
<img style="max-width:100%;" alt="" src="">
his behind

could it be a male?
Because this pinkish color on bottom?

When they were babies they all had tities so I was not shore are they all females.

No2
Likes to nib as no1 but not to bite and hates to be turned around the most, it was weary hard to take his photo and he is moving fast a lot he has pattern like father


Then there is my favorite no3, I like him-her because it doesn't not nib it is clam when handled most of all
it has pattern similar to mother

since it is calm it images came out a bit better then of the others

Can you help me with it so I can decide should mother stay with me or father depending on this baby gender?

And last one is only one I tell apart easily from others because it looks like mother but has big white stripe over head like raccoons and love milk, it was pup who was feed the best so it is slightly larger then others..
He is scared probably when I take it so it pup's a lot, so pardon next image...


I have to big aquariums so I am not giving gerbils till I can find them good home, I am interviewing friends first if some of them would take them I could visit gerbils later on or care of them when friend is traveling.
Just I have small apartment and keeping them all would be complicated but I am not ruling out that option.

Just for me gerbils smell I am
celaining with toilet paper shelves they go to wc 2 times a day. I am on the edge to buy something in store which they recommended me chinchillas that keep moist in it and makes smell less noticeable. I clean aquarium on 10 days.


Here are more images of them playing
s1048.photobucket.com/user/Erelis_designs/library/Gerbili

and one attached

[Shooting Star]

3 and 4 are female. I'm not sure about 1 and 2. One month old is usually a difficult age to sex pups.

[hesperidainblue]

Thank you weary much on your answer , I thought the same but openings looks so close on all of them so I was not shore.

I just got message from a friend who want to give them home:-) I am so happy, I wanted to give them to someone I know so in case we make mistake in sexing we can make change again. And so I can visit them