Yes, as far as The Big C is concerned, life is unfair and more precious with every passing day.
Being in a similar situation to your brother-in-law, my partner has Cancer and has been told he may see in another three years. One of the most difficult aspects he found is that friends and family don't know how to react around him...what to say - to the point some have dropped away.
Carrying on life as before has become important, all the mundane everyday things - conversations about the weather/price of butter became important - the Big C can be the elephant in the room.
On a practical level for me I found the MacMillan Nurses site online amazingly supportive, there's a group for carers, family, friends of Cancer sufferers, where you can cry, rant, rave or simply ask others who are in the same boat for advice. 