The Rose Duelists have their monsters permanently summoned into a spiritual form. Meaning all they need to do is to supply them with the energy to take solid form, rather than to pull them into our world. By doing that, there's less direct control. The monsters' own personalities mean they could be troublesome to command if you don't have some kind of loyal connection formed between them.

[He hands the deck over, as well as his spare cards, without hesitation.]

But you should be careful. I know Henry doesn't want me to know much about their skills, and he's the one in charge of their group. If he finds out you and Harriet are talking about this stuff he might try to break her away from you.