My alien race is supposed to have the ability to communicate a lot of information extremely fast, more akin to uploading something to your partner's mind than telling him. This should happen via simple touch; optimally touching hands should do it, but having to hold heads together or connect some form of "cable" will work too.
I don't want any magic or technology, maybe some kind of exchange of chemical messengers of connection of nerves or neurons. (I have little knowledge in that area so that is the core of my question.) This mechanism of communication should have evolved naturally, an optimal answer includes an evolutionary pathway to this ability.
I would also like this ability to be limited to the wider family of an individual, meaning if two individuals are more than 5 generations unrelated they should have a hard time communicating and after 15 generations they should not be at all compatible. (I'm unsure if generations is the right word here.)
Basically the closer two people are related the better this communication should work. (Reproduction still works beyond this, so abduction and rape of females to gain clan members capable of communication was historically a common practice, as were marital alliances.) Furthermore it would be nice if there were a way to destroy this ability (akin to cutting out someones tongue) to create lower class slaves. It would be great if this would damage the subject mentally.
They still have normal human senses, proprioception (way better than ours), smell and taste (worse than ours), vision (wider visible spectrum, starting at yellow and going far into UV as their star is a F-type), hearing (technically worse than ours, yet better due to denser atmosphere).
If it helps they are about 4m long and look as if Cthulhu, the Xenomorph and an octopus had a baby: each has 7 tentacles, with the tail one (climbing/hanging and locomotion, rarely manipulation) being the strongest, the lower (mostly locomotion) and upper (mostly manipulation) pair being of medium strength and the middle (carrying stuff, body hygiene and caring for offspring) pair being the weakest).
Their bodies are relatively small (slightly larger than a human body) and their heads can be turned in every direction and are quite elongated. Their home world is a tidally locked habitable moon with low gravity and a dense atmosphere. They developed in hundreds of meters high jungles near the south pole, but they have since expanded to the more moderate arid regions.
They are oviparous, but carry their young around like kangaroos.