I have a longhair female cat. I want her to have longhair kittens.Will the dad need to be longhair?

Genetics is complicated- each person/animal has dominant and recessive traits. To elevate your chances to get LH (long-hair) kittens it would be better to have a LH female and a LH male. Because both of them will have at least one part long-hair. You could get long-hair kittens from a LH female and a SH (short-hair) male too, but that is not guaranteed and the chances are lower. Even with two LH parents you could still get some SH kittens as well, you might get a mix of the two types.