Brother and Sister in Bondage by Tom Hardy
A school teacher gym coach gets a sister and his brother involved in sex, and the coach has orgies with the family and others while tying them up.  The coach is a young female.
Excerpt:
"The girl's Phys. Ed. coach, Ellen Jarvis, leaned against the wall in the gym watching the boy's PE class come trotting in. They were sweaty and tired -- and gorgeous.

She loved watching the way their young asses moved. It made her so hot she almost came. Her hand pressed against her own tight shorts. Back and forth over the crotch she rubbed. Soon, a tiny wet patch had begun to spread like wildfire. The woman couldn't restrain herself any longer. She followed the last of the young college studs into the locker room.

The smell hit her. Heavy, almost overpowering. But the maleness of it made her itch deep inside. Her cunt was screaming for some action -- long, hard cock action.

The boys were busy showering and getting dressed. Horsing around, they didn't notice her at first. She quickly slipped into Coach Barnett's office. Ellen like it in there. The shiny window looking out over the locker room was almost like a one-way mirror. She could sit in the office and drool over all the naked flesh and never be seen."

Incest and bondage erotica for open minded adults only.