Although "feral" is supposed to differ from "stray" in that the stray used to have an owner, feral cats have varying degrees of comfort around humans depending mostly on the type of place they grew up in (urban/suburban/village/etc). There are feral cats that like being around humans more, mainly because someone has been leaving out food for them, even playing with them, although they've never lived indoors. There also are house cats that haven't been properly socialized and handled, that will act more feral than cats classified as "feral".
Kittens, like all babies, are taught how to behave by their mothers. That includes trusting/not trusting humans. If your neighbor believes that feral status has to do with access or lack of access to outdoors areas, they're mistaken. It's contact with humans that "tames" cats, more easily so when they're very young, not indoor/outdoor status.
They would have a better chance of becoming friendlier/more used to humans even if they were outside (say, in a garden), but ideally in a safe place where they can observe and interact with people, see people giving them their food, and perhaps more importantly, smell humans and see they are no threat.
If your neighbor insists on keeping them in the garage, they should at least take time to introduce themselves to the cat and kittens, so as to get them used to humans.