Can offspring get hemophilia a if neither of the parents do not have it?

Yes. One-third to one-half of males with a new diagnosis of hemophilia have no family history of the disease. This can be due to a number of possibilities (most too complicated to be discussed here), but new mutations (de novo mutations) can occur in the offspring. For a good review of this topic, see http://www.Ncbi.Nlm.Nih.Gov/books/nbk1404/.
Maybe. If the mother is a carrier of the bad gene, but does not have hemophilia and she has a son, there is a chance the son could get a good y chromosome and the defective x chromosome, giving that child hemophilia. If neither parent has a bad x chromosome, then the only way to get it would be from genetic mutation.