Tatiana and Krista Hogan are extraordinary little girls. Conjoined twins are a rarity, but those joined at the head, craniopagus twins, are the rarest of all - one in 2.5 million. But it is the structure of their brains that makes them unique in the world. They have the astonishing ability to see through each others’ eyes, feel what the other experiences, perhaps even know what the other is thinking.

Inseparable follows the twins through a year in their lives and a landmark birthday — their tenth. At birth, their very survival was in doubt, and the family was warned if they did live they could be permanently bed-ridden. That Tatiana and Krista are thriving is a medical miracle. It is also a testament not only to their resilience but to a loving family who insists on treating them as normal.

Our cameras capture the tumult of daily life in Vernon, B.C. as the twins’ parents, Felicia and Brendan Hogan manage their brood of 5 with help from grandparents Louise and Doug McKay. The twins attend school, are learning the 3 R’s, and have astonished teachers with their progress. Exuberant and playful, it’s no surprise they are popular with their classmates.

Physically too they defy limitations, riding a specially built bike, zooming down hills on a toboggan, even learning to swim.

But their health remains fragile. Tatiana and Krista suffer from diabetes and epileptic seizures. The daily regimen involves pills, blood tests and insulin injections. Their mother Felicia admits it can be a stressful juggling act.

Then there are the regular trips to B.C. Children’s Hospital in Vancouver for medical tests. We follow the family as they take the twins for another MRI. They worry about a possible problem.

Dr. Juliette Hukin explains that the twins’ brains are connected through a “thalamic bridge”, a piece of tissue linking the thalamus of one to that of the other. The thalamus is a central hub which relays sensory and motor signals and regulates consciousness.

Neurological studies have stunned the doctors. Tatiana can see out of both of Krista’s eyes, while Krista can only see out of one of Tatiana’s. They also share the senses of touch and taste and the connection even extends to motor control. Tatiana controls 3 arms and a leg, while Krista controls 3 legs and an arm.

Amazingly, the girls say they also know one another’s thoughts without needing to speak. “We talk in our heads” is how they describe it.

Despite their unique connection, the twins remain two distinct people. Tatiana is talkative, outgoing and high-strung, while Krista is quieter, more relaxed and loves to joke. But she has a temper and can be aggressive if she doesn’t get her way.

When they were little, they used to try to pull their heads apart. Their mother always told them they were stuck, so they would have to work things out. But as they’ve gotten older and the frustrations mount, they still fight. As they freely admit, some days they don’t like being together. “She’s annoying,” says Tatiana, who promptly gives her twin a reassuring hug.

The road ahead will be one of endless compromise, coordination and bargaining. But it will be eased by a multi-generational clan who regard the twins as a blessing.