Disclaiming seems the obvious solution here if disclaiming does not mean that someone else gets it.
There is no CGT on the Aunt's estate other than than on the increase in value between the date of death and sale of property. (This area is complicated but it should not be a big liability)
The nephew who receives it should be subject to CAT.
Are there other assets? Does it require a few people to disclaim?
You will need a solicitor and a tax advisor to tease out the best approach.
No, disclaiming not really on as a few nephews/nieces in the family. Small cash assets to named individuals.
What will likely happen is nephew 1 inherits and incurs a liability and gifts to his sibling. Whatever tax will be will be. Merits a trip to tax advisor/solicitor.