Is the grammar correct not sure if there should be an apostrophe after the s in dads

Question

Mother planned a surprise party for Dads birthday.

Answer 1

There should be an apostrophe before the s. We add an apostrophe and then an s to make a singular noun possessive.

Dad's

Answer 2

There should be an apostrophe before the s. We add an apostrophe and then an s to make a singular noun possessive.

Answer 3

Jose said all of the multiples fo 8 are also multiple of 2. Jamila said that all of the multiple of 8 are also multiples of 4 . Who is correct