So far as his sister's share is concerned, there are no CGT implications unless her half of the sale price is in excess of the value of her half at the date of her death (which is the value used for any IHT calculation).
If the sale price (after allowing for sale costs such as legal and agents fees) is higher then he will almost certainly have to pay CGT on the difference between the two values unless is is under his annual CGT allowance (currently �9200, I believe). It is possible there might be some reduction because he lived in the house for some time, but I doubt it because it is his sister's share not his own.
So far as his own share is concerned, I believe his CGT liability will be based on the value of his share in 1982, updated for inflation and taper relief. There will almost certainly be some allowance for the fact that he occupied the house for part of the time. This area is complex and he will need to get professional advice.
The Government is proposing to change the CGT rules and the effect may then be quite different.