those bombers woke us up in the twilight at dawn
twi·light noun, often attributive \ˈtwī-ˌlīt\
: the light from the sky at the end of the day when night is just beginning
: the period when day is ending and night is beginning
: a period when something is ending

The policeman wore a (service) cap with a cornflower-blue frock
frock? I think this is called 'crown' (тулья).

with strange tommy-guns in hands
I should probably mention that submachine guns weren't very common. Soldiers were armed mostly with Mosin's rifles.

Grammar here (no subject, wrong word order, wrong tense):
Peter yanked it open; (subject? he) only by chance (did) not torn tear it off the old rusty hinges
He did not tear it off the rusty hinges purely by chance.
or:
Peter yanked it open nearly tearing the rusty hinges off.

Choice of words:
he quickly banged it shut
'Bang' comes with a very loud noise. Peter did not want to be heard so he should have done it quietly.

seemingly still absent-minded
... still in shock.

Grammar (this worked most of the time - just Past indefinite):
he saw in a movie that a slap in the face had worked in this way

She awkwardly tried to crawl into the barrel. That She was so very slow that Peter just grabbed her
Grammar (no subject):
He covered the barrel with a bunch of rags (subject?) found here in the pantry
either 'he found here' or 'which were lying here"

Plot:
When he heard the street-door open he just kneeled, squeezed himself in another corner and also covered with the remaining rags
So many rags. I'm trying to think why would anyone store rags in a pantry?

Quieted down, he was sitting sat there in the corner watching through a small hole he left in his cover.
The man finished the inspection and went out not bothered bothering with closing the door.
However, they kept sitting in silence for yet another ten minutes
Consider rephrasing:
her shoes were soaking with liquid with tiny pieces of something stuck all around.
‘Wasn’t that it empty?’
Plot:
‘Mushrooms’
50 gallons of mushrooms!? Well, ok. I wonder how long it takes to pick so many. Besides, you'll get poisoned if you try to eat them anyway. When you pickle something the container is supposed to be hermetically sealed.

Peter chuckled and took a quick look out of the pantry
... cautiously peered out of the pantry door.

took a sit in the middle of the room
on the floor?

Choice of words:
‘you can give us away with the heaving movement.
to heave means lift, raise, elevate, to rise and fall (like a wave).

Their group are one of the pioneers advance parties
‘I got it, go on.’ he said pensively.
pensive = musingly or dreamingly thoughtful. Just thoughtfully will be better. He's not very melancholic right now, quite the opposite probably.

they have found the a Russian soldier at in the village
Better split this sentence in two:
Peter never had served in the army, he wasn’t a special forces officer. He wasn’t a martial arts master either.
What do you mean here?
fights with other terrors like him
because contemporary business world obeys follows the same cruel rules
Inconsistency:
and rushed to the main room
I thought they already were in it.

a couple of pretty crappy knives
Pretty crappy? LOL.

and crouched out the door.
He did what? Crawled maybe? crawled out of the door?

Peter found a place off the view out of sight of both the guy and the girl and sat there
Plot:
He caught an appropriate moment, jumped on the guy, covered his mouth with a hand, yanked the guy’s jaw up to open the neck and cut it open, still holding him tight in a grip with both hands and legs crossed round the guy’s waist to prevent him from either screaming or moving.
... and now the whole village's going to be killed as soon as somebody misses him.

Peter covered her with her rags , grasped by the hands and dragged to into the house.
Rags again? Clothes maybe?

Having done with the girl he turned to Ann:
Not done, that sounds as if he did something permanent to her . Say something like 'He gently laid the girl onto the floor and turned to Ann'

Ann nodded and the last thing he saw leaving was the same thing he had been doing to her an hour ago before: she was slapping the girl in the cheeks.
A whole hour had passed? I thought it was merely several minutes.

Rephrase:
Peter came over to the body and started to look through his belongings sorting them
Not Peter's belongings, but the belongings of the dead soldier.

a water bottle a flast of water, something looking like a first aid kit, the boots
a flask or water. Certainly it wasn't a bottle.

I just don't understand this sentence:
He just bunched the things together on the clean side of the guy’s shirt, rolled it up
The only 'clean side' of the shirt would be the back one. Rolled what up? The shirt? Whatever for?

By the time he returned Ann had managed to bring the girl round to her senses, they had even found some clothes and now were sitting on the bench and talking. When he came in Ann said ‘We’re ready to go’, but suddenly added: ‘wait, I’ll get you some clothes’.
A minor notice. Consider changing 'talking' with 'sitting on the bench with Ann trying to comfort her.

Plot:
trying to find a bag or something to keep his new stuff. He was done had finished packing just before Ann came with the clothes.
What did he find finally?

He briefly examined the tommy-gun submachine gun and suddenly realized that he had no idea on how to use it.
If you want to stress out the fact that Peter calls it so because it bears some semblance to the real tommy-gun then put it in quotes 'Tommy-gun'
Although, it was unlikely those soldiers had PPShs. It should be Mosin's rifle or a Mauser (German).

‘I don’t, wait I’ll ask Dasha’, she said.

Plot:
The girls were chatting for less than a minute, then Ann said ‘Yes, she knows. She is married to an officer and she has seen many times how to shoot and reload when they livied at the military camp.
Hmm, not very believable, but it's your story. Don't you think that some description of how Dasha looked might be in order. How old is she, what's her hair color (oh, almost forgot - I don't know what's Ann's hair color also).

‘Okay, better than nothing; I think guess she’ll have to teach me,’ Peter said slightly embarrassed by the fact that he has to learn from a girl how to shoot a gun.
Some other thing: where's Dasha's husband? Did she wordlessly agreed to follow them? Didn't she at least ask just who the hell was this foreigner who'd just killed a man who tried rape her?
I think she could say at least 'thank you'.

‘Not a problem,’ Ann said, ‘When we stop for a stand she will teach you.’
Stand? What do you mean?

By the way - where are they going? Shouldn't they discuss it?

oh, ok. I'll continue later.