The pens we use for fatteners (usually only 3, or 4 at most) are 20m x 20m and after 4 months they're usually fairly trashed
If your fruit trees are less than 10 years old you'd be best to fence them or protect them somehow from the pigs as they
probably will damage the roots with their digging (or, worst case scenario dig 'em all up for you). The whole area might end up very wet & muddy depending on what the weather is like in your area? Clay soil, rain and pigs isn't a great combo I'm afraid
We're in wet, central Scotland (on good, though not very well drained soil) and with the weather as it has been for the last year we're actually rotating twice as often to reduce damage to the ground. If the weather in your area is quite good, you might not need to move them out of the original area - but if it gets quite wet you'd be best to have a stand-by spare pen to make it a less horrendous experience for you and the pigs
Pigs & chickens - well, lots of them live happily together but I dare say a fair few chickens have become a tasty treat for the occaisional pig who was fast enough. Pigs are omnivores (eat anything) and no-one's told them they've not to eat meat
I kept mine seperate, but we did have a wee hen who used to come and roost in the shed around the farrowing pen - she wasn't ever eaten
HTH
Karen