They treat her well and overall take things very lightly, but I do wish the three of them would at some point declare she's a party member and not a slave, or something along those lines. For now they've continued along with it, and while they're obviously not malicious, cutting out the root of her insecurities seems just like what Minami needs right about now.
If anything, we'll probably eventually get a chapter in which she's explicitly "freed" and given the choice to stay with them of her own accord, maybe, and the guys seeming so nonchalant about everything still is just emphasizing how food-motivated they are.
Also, just yeeting a wok full of boiling oil is CRAZY.