You have to get into their good graces first. In a future update, I should change it so you can ask and they reject you.
ah but you see that was at the beginning of my play through before i helped either of them and even after helping lucile increase her milk production i still could not ask her to the tasting. also with susie and susanne i could not ask about their games to marline when roxanne mentions she should ask marline them about there is just not yet an option to ask about susie and susanne yet and i only managed to beat them on my own through perseverance so i'm not sure but maybe could be a bug? also i didn't realize that talking to susie after marline mentions it was a seemingly random event and got confused as i could not flat out ask if they were abused and asking about their childhood and the cooking got me nowhere so may want to make it clearer
So, as it's coded, there are three conditions in order to invite Lucille to the party. They are: you've discovered Lucille's interest in anime, you've established with Peach that you're going to start inviting people and there's an active time limit before the day of the party, and it's evening when you talk to Lucille (That's when she's most willing to talk about anything besides anime.) As for asking Marline about Susie and Susanne; the way it's coded... hmm, yep, that's not right. The way it's coded: if you DON'T ask Susie and Susanne about their milk production before playing the game with them, the option to talk with Marline about them WON'T come up. You could however win against them to clear the condition of there being a challenge, then ask them about their production. The story will look very confusing from there though. If you do this, the option to talk with Marline should come up.