Issei's parents have very little hope in him through out the series and see him as a pervert who will never get a girl, often referring to him as an “incredibly horny child”. It seems that a lot of the problems they face with Issei are caused by his perverted nature, shown after Rias heals Issei after being stabbed by a fallen angel the previous night due to Raynare’s failure to kill him. As Issei is shocked as to why Rias lies naked in his room he panics as his mother walks up the stairs. He frantically tries placing a blanket over Rias to hide her, but his mother walks in and starts yelling at her husband as he brainstorms all the possible perverted things Issei could have done to make her react that way. But to there surprize when Asia moves in it gives them hope that they might have grand children.
Issei’s parents tried three times having children, the first two were tragic miscarriages, meaning Issei has two unborn older siblings.
Issei’s parents were easily swayed into allowing Rias to move in with them as she says that it will enhance their grades by being in close proximity. Later, all female members were commanded by the Great Devil King, Sirzechs, to move into the Issei Hyoudou residence.
As of Episode in the anime, it is shown that Issei’s parents have taken into liking Asia Argento, who moved in with them under command of Rias Gremory. In episode it is shown they are taking photos and videos of Asia. It was later on that they would meet with Rias’ father, Zeoticus Gremory. They befriend one another and Issei invites him and Rias’ brother, Sirzechs.
As of Episode 12 in Highschool DxD New, Rias asked her brother Sirzechs to remodel the entire house to accommodate all of the members of the Occult Research Club. Issei’s parents were seemingly oblivious to the fact that it is physically impossible to remodel a 2 storey house into a 6 storey mansion. They claim that they were “glad to have slept through the entire remodelling process“.