Mashu Takahashi vs Mashu Taneda: battle for Papa Senpai.
And Gudao is being an idiot by letting it continue without even talking to Mash. This sort of thing doesn't just sort itself out on its own, not unless its an h-game with a harem route
I think the devil blood she probably used to conjure that girl is taking over. If things continue at this rate, their daughter is going to grow up into a real succubus.