Retro 70s Porn: What's The Movie?

So, just looking for the name of this movie - as they were actual movies back in the day, and this particular stag film starts with family eating breakfast with mom's professor boyfriend talking about witchcraft - and the movie ends with a Satanic gangbang (because 70s, LOL)

I've seen the whole thing ages ago, but no idea about the movie name - and can only find a few scenes like pictured