I was getting a little worried, as I've seen the mom cat two times this past week, but not the kittens. So today, I went to ask around, and it turns out that they're living happily in the workmen's huge shed. It's below the "office" and has a wooden floor and lots of places to lay around. I spoke to the office woman and a few others, and it seems that one of workmen will take the kittens when they close it all down in October. Not sure he'll also take the mom, but in any case we'll find a solution - and at least get her sterilized.