It's easily possible, the main problem stems from where will they get their money from if the guy is busy giving her 7 daily steamy love making sessions.
Honestly low-maintenance succubus considering we don't know how much does the magic draining part affect the whole thing.
In Praying Mantis case it's been observed that biting the head off happens a lot less if the female isn't stressed, such as being observed by gigantic 4 limbed meat creatures, and as long as they're not hungry or starving.
Azazel family heavily suspects but neither of them is 100% certain he's human.
Ameri suspected it at start and was going to push until she found out but is now so deep into their relationship she doesn't care.
Henri still suspects it and is wary of Iruma being human, until Ameri comes up in the...
Mafia Iruma didn't spend his childhood in constant danger so he doesn't have Absolute Defense that he has in the main series.
He's a loved and coddled little grandson in this series.
He doesn't have Delkira's mana, he has Delkira's ring which has a fragment or entirety of Delkira acting as Alikured within it, Sullivan or Opera feed Iruma's ring whenever it's empty and the ring converts their mana into Alikured mana.
Hopefully Sullivan did choose Iruma at random as first...
Mephisto is so old most others probably don't even know he exists as that, and why he's referred as "Mind-games king", he literally chose not to exist while Delkira was the acting Demon King because of how perfect Delkira was.
She greatly suspected that Iruma is human but decided she doesn't care and probably considers him a demon since the question didn't come up for a long while.