Thanks for your replies and links.

The three kitties have been spayed/neutered today, it went well. We forgot to ask who was male/female, but we'll know tomorrow.

The plan is to put them all in a huge cage with litterbox and everything, and my neighbor will take them for a while, until they can be adopted or be with other kitties. I know she can't bear to keep them in a cage, so she'll probably let them out in her flat - we'll see what the Cat Rescue woman says. Two of them are definately siblings, not sure about the third one, but they have grown up together and slept together in that workshed, so I'm sure they'll get along.

Will tell you more when I get news.