Hi Searchlight, I guess no-one can say for sure if the kitten will become less feral if taken home, but if it's any help, I currently have x2 1 year old cats whom were rescues from a farm at 10 weeks old (as the farmer used to shoot any excess cats) by a rescue centre.
Themselves and their parents were completely feral and they wouldn't come near us for a couple of weeks once we had brought them home and installed them in a nice warm safe room.
It took a long time, quietness and patience to get them to come out from their hiding places - but after spending as much time as possible with them before and after work each day and teaching them that humans are ok after all, it worked out.
They are now very cuddly and playful cats who love being outdoors, come to a call and get on with our older cat without issue (the older cat was also a feral kitten who was dumped in a box a few years back - she's turned out fine too).
If the cats are left, yes, they would be able to eventually fend for themselves somewhat, catching mice & birds and going through bins, but what if you ever leave the offices and they become dependant on your kind tid-bits? What would they do then, and what would happen if they get injured? If they grow up feral, they wouldn't let anyone near them to help.
I know you aren't daft and care about them, but I can't tell you what to do - In an ideal world, I would try and catch the mum and kittens and take her to a vets to see if she is microchipped. A lot of pet cats can be extremely wary of other humans, so they may possibly be owned - Check this as a first point of call.
If not owned, and if it was me, (and only if they appear to be old enough to leave mum - eating solids, about 8-10 weeks old) I would take the x2 kittens home as pets. This isn't for everyone though as kittens really do destroy wallpaper/ sofas/ curtains and these will need litter trays providing/ emptying - and will need a lot of time spent to get them tame.
The mum will continue to breed more kittens if left, and the kittens too eventually, so perhaps you could get in touch with a local sanctuary and see if they can assist? They may be able to take all three on and neuter them all.