I was executor for my mother's estate in similar circumstances and we got valuations from 4 different agents and then agreed a value amongst ourselves. However, this was in different times ...
Consanguinity relief
This relief applies to transfers of land, buildings etc. to certain relatives, e.g. parent, grandparent, step-parent, child, foster-child, adopted child, brother, sister, half-brother/sister, aunt, uncle, niece, nephew. Duty is charged at half the normal rate of duty applies so if house purchased for € 150,000 stamp duty is due at 1/2 of 7% on the portion over €125,000 ie €875