How old is your rooster? If he's very young or very old, he may not be fertile. Do you know how to check for the bulls-eye in a fresh egg, to make sure they're getting fertilized? If your rooster is still a youngster, he may just need time to mature. If not, you may need a new roo. You could also give Momma some fertile eggs from elsewhere, next go-round.
Good Luck!
EDIT to ADD - If Papa is a bantam and Momma is an Australorp, it's quite possible that he simply can't reach. 'Lorps have all those fuzzy tail feathers, so your little rooster may have a hard time making his ... ummm ... presence(?) known!