I don't know for sure, but I did find this Scientific American article -
Manipulative meow: Cats learn to vocalize a particular sound to train their human companions and this Live Science article -
Why do cats meow?
Maybe not quite what you are experiencing since "your" cats are strays and it sounds like they are keeping their distance from you.
We do have a stray female cat that comes around, we call her Momms Kitty because at one point she had 3 kittens following her around. She has been coming around our backyard for a little over 2 years, and she is slowly, over that time, getting more socialized. But even though she still keeps her distance (outside of a short sniffing of my fingers and a brief face rub), she will act playful and rub up against the wooden railing beside the steps - so she reacts like she wants to be around people, but she is still very cautious. And it has taken upwards of 2 years before she got this friendly. So I am not surprised that the stray cats that are at your place are still skittish.
Oh, the ones here will get comfortable really soon if I start feeding them. It will only take a little milk 3-4 times a day, and they will allow me to pet them as they are drinking, and then run away for a couple of days, and inside 3-4 days they will get cozy enough to allow petting even after they are done with their milk. Full comfort will take slightly longer, that's it. I know people around the world talk in terms of years, I really never could get that. It might depend on species of cats?!
Yes, I knew about animals manipulating, learning what triggers humans to their advantage, be it food or play, or anything else they want from humans. Dogs do that, cats do that, I think even birds will do that, parrots and such. That is why I was wondering that since these are currently stray, and I have shown no inclination towards them and rather I went after them yesterday night itself to get them out of the compound (because they just keep eating pigeons and we need to clean the feathers up after them), they would not be mewing to manipulate me. So, I thought that these sounds are probably just their hunger coming out loud? I say this because I know they are ill-fed for sure, they rely on tidbits here and there or the pigeons they might catch.
Also, this thinking comes from experience. 3 years ago a mother cat delivered 2 kittens in our compound, and we fed them 3 times a day. Since they were never in the house, the mother would roam out and about, and kittens would generally just stay close to the house and in the compound, if anything. Occasionally they would leave with their mother come back anytime. After a while of this, one day I suddenly had to take care of the two kittens myself since the family just disappeared for a few days and later the kittens somehow managed their way to our house again.
So, my observation was that if they are fully fed, not hungry anymore, particularly at night, they would not make any noise at all. We would feed them last at around 9-10 PM, play with them a bit, and then go sleep. They would sleep in a makeshift arrangement I had created for them in a corner in the compound. Zero noise till 7-7:30 in the morning, when they will start making noises and try and wake us up (climbing in windows where they could peek inside, etc.).
This is what makes me think about this stray family, that are they making noises because they are hungry, or is that just their family discourse! ?