I don't know what it is to help. For others it would help if you tell us if you have added any fertilizer or anything to the soil .

Did you look at the pictures? Doesn't that look like some disease or pathogen (mold/fungus)? Or did you mean that there is no hope at all with: "I don't know what it is to help."?

Just a "sparse" (small concentration) solution of fertilizer (but I don't know which/what as my great aunt gave it to me in a bottle with no label - supposedly some natural eco fertilizer. I didn't want to fertilize actually as I believe our yard soil is quite rich. Although contrary to my belief I did add some wood ash too. :P But I would not think that the problem is arising from fertilizing the plants as not all are affected (currently only 3 out of 14)...

Is there late blight in your area? If it is LB, I don't think there's anything you can do about the affected plants right now. For the ones unaffected, you might want to start a spraying program with a copper based fungicide.

I just meant that I don't have the knowledge to identify what is wrong.

Looks like late blight.
Facilitated by overhead water -- rainfall or from a "helpful" gardener -- during warm weather.
If so, you'll know soon enough because the plants die in short order.

It really might be late blight upon better inspection and reading about it on the internet. And yes, many people have the same problem. The weather last two months has been exceptionally good for molds and similar. Not so hot as it should be, lots of humidity and loads of rainfall.

So the best thing is to remove the affected plants to minimize the possibility of disease spreading to other plants?

Is there really no chance in them surviving this? And how long does it usually take for the sick plants to die off? A few days, maybe a week or a couple of weeks?