Here are the possibilities of the baby having PKU in your given scenarios:
If one parent is not a carrier and does not have PKU none of the babies will have PKU, because both parents need to pass on the mutated gene. There is no way to be certain what the chances of your friend giving birth to a PKU child is, because although her brothers have PKU we do not know if she is a carrier or not. She would only have a child born with PKU if she is a carrier and she marries a carrier.
For question 5, there is a 1:2 chance that your friend is a carrier, but 1:40 that her fiance is (unless you are in a country where PKU is more prevalent). If the fiance is a carrier then there is a 1:4 chance they would have a child with PKU. The statistical probability between being her being a carrier, him being one and the child having PKU is 1:320