When calculating out Capital gains tax - normally you can deduct the initial value from the sale price as well as the cost of any home improvements as well as a deduction which will vary depending on how long the property has been held.
However, I think that in this case, it is the difference between the value when it was passed to the 3 receipients that would be deducted from the actual sale price. This when spilt 3 ways would be a capital gain.
I would suspect that in this case, the gain would normally come below the individuals CGT allowance. Whether there would be any tax to pay would depend on any other capital gains made in the year by those individuals and the amount of the gain made on the sale.