Michael - you are in an awful position, I can see.
You need to get legal advice as soon as possible. Make an appointment with your solicitor or go the the Citizens' Advice Bureau.
Before the appointment - make a note of everything that has happened, including dates. Just a simple timeline to help make things simple.
Take all relevant documents - the title deeds, the charge, the will, and everything else you can think of.
On the face of it, your brother in law has the law on his side, so you do need all the help you can get.
There may still be a way of releasing equity in the house to pay this debt off. �23000 is a lot of money, but not compared to the value of the house. It is a 'safe' loan. I don't know too much about reversion schemes and so on, but CAB may be able to help with that too.
This is an example:
http://www.learnmoney.co.uk/equity-release/rev ision-1.html
If you are old enough there may be equity release schemes suitable:
http://news.bbc.co.uk/1/hi/business/3040663.st m
Both of these are 'last resort' things that need a lot of thought and advice.
Repossession is the very worst thing though - if you have no other option you should sell the house yourself. You will get much more money for it that way - but time is not on your side.
I can only stress how important it is for you to get proper legal advice as soon as possible.