Backstory
David Johnson and Wendy Rosen weren't always conjoined. They were born perfectly normal taurs on the same week, their parents marrying when they were only eight. David and Wendy got along quite well and played with each other often. However, during a bring-your-child-to-work-day at the family's local laboratory, the two kids started playing around experimental portals. Their parents paid no mind at first, since the portals were stable with individual tests. However, the two kids crossing different sides of portals started causing fluctuations, until they both crossed a single portal from opposite sides. The next thing the two knew, they were waking up in a hospital, conjoined to each other, their rear halves fused similarly. It took them many months of physical therapy and studies of their new combined form to understand and accept what had happened to them, the teleportation technology deemed too dangerous to attempt to defuse them. Over the years, they've gotten used to their situation, becoming very skilled at moving in tandem, getting around just as fast as they used to. Almost 20 years after the incident and the duo are physics teachers, their own personal experience with quantum entanglement helping them excel in their education. As for their rear, it wanders the fields of their cousin's farm, safe from any harm and thankfully requiring nothing to eat.

Anatomy
David & Wendy exist in what can be summed up as quantum quatrefoil blending. In other words, despite their bodies physically being connected, they are still "connected" to their rear ends, resulting in any fluids and solids transferring from one conjoined body to the other, not from one end to the other. David & Wendy can feel each other's half up to the base of their upper torsos, but cannot control the other half. The same goes for their conjoined rears, which also move through base instinct, meandering without any input from the two.

If you have any questions, ask below. I'll be sure to respond and clear up any confusion.