We had a similar situation in our backyard some years ago - before we got Fister. A cat had given birth to 5 kittens in a box attached to someones bicycle. We didn't know how the owner would react to that (the box was used to have a child in, while cycling) so a group of us build a house and put blankets in and put the 5 kittens in there. The mom saw it and followed us to her new house and moved in. But sadly, she would not feed them. We all checked 3-4 times a day, but after 3 days, the ones having cats themselves, decided it was the best to have them put down. She totally neglected them. We think the reason was that we'd touched them. Really sad!

I hope you'll find happy homes for them, when they're old enough! - 12 weeks!