If there are 3 players you want, you have to list all 3. If your top player is there, you will get him. You will not get the other 2 unless you copy over your list to the next round. You can save up to 4 rounds of picks with each waivers. If you want 4 players, you have to copy it 4 times, I think there is a button you can click to carry over your list to the next round.
If there are 3 players you want, and you only have 2 roster spots, make sure you are dropping someone for the 3rd round of waivers. Do not drop anyone with any of the players in the first 2 rounds, as you have to roster spots open. If you enter a 3rd round of picks however, you will need to drop someone in that round to pick someone else up.
If your roster is full, and you don't list a player to drop with your pick-up, then MFL.com will deny your waiver. This is not a decision the commissioners make, MFL.com automatically rejects any waiver requests that will put a team over the roster limit.
Here would be an example for 3 players wanted, with 2 open roster spots:
Round 1:
Pick up Player A and drop none
Pick up Player B and drop none
Pick up Player C and drop none
Round 2:
Pick up Player B and drop none
Pick up Player C and drop none
Round 3:
Pick up Player C and drop Joe Shmoe
You might notice that the first player from each round does not have to be carried over to the next because if that player was still available, then you would have already received him. Notice in the 3rd round that you have to list a player to drop, because once you pick up the first 2, then you have reached the roster limit.
HTH