the parents part couldve better written instead of making them retarded. moreover mc looks like reasonable civilized guy, tell them your story
"mom dad im a reincarnated person, back then im the king of demons, we and humans was always at war so i did....etc. "
"im sorry if this is out of your expectation but i still consider you two as my parents to some extent" (he did say its nice to have family)
" how is human demon relationship right now ?, as i am supposed to reincarnate within demon bloodline, i assume theyre in peace no ?"
or something like that