Hemophilia a is a sex-linked recessive so that means the mothers never have it?

Not always. Hemophilia a is a x-linked recessive gene. It means if a male has the defective gene, because they have 1 x and 1 y, they will have hemophilia. In order for a female to get it, she would have to get 1 copy from a carrier mother and a hemophiliac father. She would then have two copies of the bad chromosome and would have hemophilia. The chances of a female getting two copies is less than a male.