You will have to get a licence to take them out of the U.K. You should only need a net to stop birds taking your fruit, I can't see any cross pollinating except the apples.

Birds shouldn't harm the trees but I would wonder about them being in pots for three years; can you not plant them in the ground and let them grow? I also have doubts about how well they will do being taken from cool, damp Yorkshire to hot and dry Portugal. I would have prefered to buy locally.

I agree with the comments above and those on your second asking of the same question. Please don't double post we get enough questions as it is.