I’m not a realtor nor a lawyer, but recently filed a PC Exclusion myself, so looking at the pamphlet…
You said they obtained the property from their parents but didn’t specify if it was an inheritance or transfer or sale or??
If the parents simply transferred it, and they (parents) also applied for a Reappraisal Exclusion for Seniors on their next residence (assuming they just moved from that house to another), it seems the children couldn’t apply for a Parent-Child Exclusion on the transferred house. The parents would have transferred the low tax basis to the next property.
Also, regarding corporate holdings or partnerships, they appear not to qualify for the Parent-Child Exclusion. But properties held in trusts do seem to qualify.
Again, not an attorney, so ask an attorney if seeking legal advice!
