It depends on the focal length of the lens. To be safe, double the (35mm equivalent) focal length of your lens in mm. You were shooting a full frame camera with 35mm lens = shoot at ~1/70th and don’t worry. With good technique and non-moving subjects, you can slow the shutter down even more.
Shooting 1/125 on a lens that short because you’re worried about motion blur is very much overkill.
In order not to become a thread hi-jacker, I started a new one here:
Have fun!
Claes in Lund, Sweden
I totally get that, and in fact have been on board with that idea myself. It’s not for nothing that I went for the size advantage of Micro Four Thirds. However, I will say that it is in exactly this same kind of conditions that I have come to the realization that the ONLY solution is to change the lighting. The easiest way to do that is with a small speedlight. Luckily, there exists now some very small and portable options (also affordable). Check out the Godox TT350 (http://www.godox.com/EN/Products_Mini_Camera_Flash_TT350S.html). It’s pretty affordable at about $85 on Amazon (here in the US),. You get the version that matches your camera brand, and it will take advantage of TTL (through the lens) metering, meaning that it’s a breeze to set up and use.
I think in this situation, even just mounting a flash on the camera with a diffuser or a bounce card and a warming gel to match the ambient lighting (so you can adjust white balance globally) would have really helped your subjects to pop, and allowed you to use a lower ISO for a cleaner result in the end.
I have resisted adding flashes, etc, to my setup because I just didn’t want the added complications of that. But I am realizing that if I “want the shot,” then under certain conditions you need to bring your own light. We all love post processing, but there is only so much one can do under adverse lighting in post.
EDIT: just a little example showing how using a small on-camera flash with a little diffuser can make an impossible photo possible. This is from our recent christmas fair here in my town, and was taken right at dusk, pretty much in the same (or even a little darker) conditions as you photo. Artificial lights abounded, so it would have been possible to take a shot in the ambient conditions. But I opted for fill flash so that my wife and baby would look like human beings, and not orange ghosts, lol!
Here is the absolutely un-edited (SOOC JPEG):
Afraid of the grain, chuckukkhh chuuuhhh, no no it’s more like john voigh in runnaway train, a beast meeting its destiny, through the cold, fighting with broken greasy hands, with a broken soul, fighting for what? to die a free man… maybe
This one doesn’t have any noise reducShionism whatsoever > RT_RC2
ND7_5227_P_bonheur_02.jpg.out.pp3.zip (4.3 KB)
Edit:
Now looking at it, it’s a bit flat a maybe too warm. Anyway a photoflaco version, laso no nr either
Full size denoised image (it’s a bit soft)
and then I’ve tried to use 2x2 pixel binning in imagemagick
http://www.imagemagick.org/Usage/photos/#binning
magick convert ND7_5235.tif -resize 2142x1422 -filter Box ND7_5235.jpg
@age thank you this is great. great improvement over mine. will use it.
This is great! I’m so happy about this for a bunch of reasons; obviously that I found a way to make these portraits work, in spite of the yucky noise, but also that things got solved by our little community here 
Tried the new RawTherapee 5.5 with this image. Here is the result.
ND7_5235.jpg.out.pp3 (12.0 KB)
A try using darktable 2.6.0rc2 with the new filmic and updated color balance modules
Totally Off Topic, but have you noticed that the S-cube is up-side-down?
Have fun!
Claes in Lund, Sweden
@stefan.chirila If I am able, I might try going there to take some photos myself.
Both are. I wish the third “S” were a “D”. They were just kids yesterday… 
Gulp. I missed that one 
The tiniest strobe can have a massive improvement, especially for short range stuff like portraits. Also they can be set and forget automatic. Set you exposure on your camera a stop slower (800 rather than 1600) set your strobe to the correct metered value (1600), and pop away. A simple move like this takes half the light from the strobe, half from the scene. Experiment with more and less fill from your strobe and have fun.
Happy holidays guys (and gals if any) 
Sorry for the late feedback @stefan.chirila
I had a lot to do in the last weeks and couldn’t answer.
I didn’t use RT but darktable and only rudimentarily for white balance and noise removal without base curve.
For white balance I have chosen a small grey dot from the woman’s shawl
I did most of the work in GIMP and yes, I have done selective edit by splitting models and background.
I treated them separately.
The idea was not to process the photo itself but simply to show you how I imagine the result in such a situation. 
That was all in RT. I shifted the hues of the yellow wall behind them closer to orange, since that is closer to their red jackets. I white balanced off of the guys grey collar, but I thought it was too yellow, so I made it a little cooler than that with the WB slider.
Yeah, it’s amazing how it seems possible to bring a corpse back to life with a dash of orange - in my experience. Let me hasten to add that this couple is quite alive and looking much better than that! 
I know the orange-shift trick is maybe the easy way out, but for some underexposed, artificial light stuff it seems to be necessary.
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