Are you asking a very specific question here? As in, would there be an exemption if "they were left the main residence and another property."
The wording on the Revenue website is clear about a single property
"The recipient must not, at the date of the gift/inheritance, be beneficially entitled to any other dwelling- house or to any interest in any other dwelling- house. The Revenue's view is that a dwelling-house means a building or part of a building being used or which is suitable for use as a dwelling. "
If a recipient got two houses, Revenue might take the view that there was no hardship ( which is the point of the exemption) and say , pay any CAT due. I don't know - I have not come across that scenario.
mf