I have got 4 plants in the same pot from one month ago, on one of them there is a flower.
I'd recommend leaving them alone apart from ensuring the pots don't dry out. One month is too early to call a lack of dew a serious problem. If one plant is flowering, your conditions can't be that bad. Besides, you may wreck the happiness of the one that is doing well in trying to fix the others. After reading this, I definitely recommend doing nothing.
Capensis is a weed. If you have one flowering, you can afford it if the other three even die (not that I think they will). You'll soon have more capensis than you know what to do with. Including in pots where you didn't plant them. In the sense that you aren't at risk of not having capensis anymore and take risks due to some perceived urgency. You can afford to wait.
Temperature is constant due to central heating and it's 23 C.
This sounds reasonable. I don't know if capensis prefers a night temperature drop - mine doesn't seem to care much either way, but if they get some sun in centrally controlled temperature, they will get a slight rise while they get the sun, so some natural fluctuation will be there. One thing to consider may be that the humidity is too low, which is why they aren't dewing up quickly. So it may not be a problem at all, and with more time growing, they will adapt and have dew or they will with brighter light in coming months.
Some say to increase it with bags and such, but my experience with bags is not so happy (I live in a hot climate and any plant without ventilation is an unhappy plant here). You may want to leave some water in their tray for a slight humidity boost at best.
I use distilled water from the shop and I am not watering directly in the soil.
You could try top watering. My plants seem to like it. I avoid watering on the flowers, and maybe avoid the leaves if I am in a careful mood, but they don't really care so much. Top watering will keep your media free of dissolved gunk. But I don't think this is an issue with your plants.
I fed them with insects while they had dew and that went good as far as I can see.
Don't feed them now.
Plant with a flower have red leaves, other three have green leaves.
It seems to have adapted better than the other two.
In my part of the world now it's winter, but they have 10 hours of light every day, and if it's not cloudy, they have 6 hours of direct sun light.
This seems reasonable for the season - 10 hours of light seems on the low side in terms of duration, but 6 hours of direct sun seems good. Maybe artificial light for a couple of hours till bedtime?