These bets, along with the other proposition bets have horrible house edge values. Their only advantage is that the player can break the monotony of playing all the time pass line with odds, by making a hardway bet.
Making a hard way means to make the total of the two dice on doubles. Say you wanted to hit a hard six, the only way to do it is with two threes. Why is it called the hard way? Because it sure isn't easy to win anything on it. There are only four hard way combinations: 4 (2x2), 6 (3x3), 8 (4x4), and 10 (5x5).
These are not one-roll wagers. Hard ways win if the selected hard way is rolled before a seven appears or an "easy" combo of the hard way total is hit. So if you have a bet on a hard 4, if a 3 and 1 comes up before two twos you're out of luck.
The payouts for hard four and hard ten are 7 to 1, and the true odds are 8 to 1. The house edge is 11.11%. The payouts for hard six and hard 8 are 9 to 1, and the true odds are 10 to 1. The house edge is 9.09%.