Actually, I've seen that happen with barn cats if one cats kittens all died shortly after giving birth. They will hear the cries of the hungry kittens and come in to help out, relieving them of some of their milk (which can cause problems if they have to dry up suddenly). They look to me to be around 4 weeks old, so Princess may have started the weaning process already, especially if they are showing an interest in kitten food. They do look exceptionally healthy for kittens born outside.
As for socializing, just spend as much time with them to get them used to humans. Their curiosity will get the better of them and they will feel comfortable with you in no time at all.