My understanding is that ANY asset left in a will is taxed on the basis of a "hands off" valuation.
Ir doesn't matter if it is art, property, classic car, wine, whatever, the value of the estate is calculated and death duties paid on the value above the threshold.
If you have monies in a SIPP it can be passed to someone who has a SIPP, without taxation. But of course when they draw it down it will be taxed...
The only way to avoid inheritance taxation is to die penniless is to gift the money now and live 7 years.
Would you give your son your house? Remember, he can evict you and make you homeless...
