Well done weighing one! That’s great news it is already 400g and not a real tiny one – and lucky you got the small one so more re-assuring that the bigger one might weigh more already. At that weight and bearing in mind the mildness of the weather and that they’re turning up regularly for food (and water), I would let them stay ‘in the wild’ for now and hopefully they’ll soon put on a bit more weight. You providing food for them makes all the difference. Good luck little hogs!