Actually Iniss 226 might not be so much not caring about being the ideal father because he does, after all, have to fool Melissa, but he is probably incapable of feeling any sort of affection for the girl, he also, probably, sees her as a nuisance since she's the only non-controller in the house and Chapman has made it clear as early as book 2 that she'd best be remaining that way or there'll be trouble, so Iniss probably blames her for things like not being able to talk freely, or even having to play human at all when he's in the privacy of the Chapman home.
Visser One on the other hand had kids of her own and had been a human controller much longer, I'd imagine her the better actress, and she says she chose Eva in part because she was a mother so she probably wanted to play mother with Marco since she couldn't have direct contact with her own kids. In book 2 Rachel says the Chapmans are saying the right words but they're not feeling them, so that might be the problem, maybe if Marco had been older he would have noticed a problem with his mother.
