Gerry
A person can not be held liable for another person's care fees.
A spouse is entitled to will his / her property to whoever he or she desires. It will then not be the property of the person needing care and it can not be used without the consent of the beneficiary.
If a house is in the husbands sole name and he has to go in to care it is unlawful to sell or put a charge on the property at present even if it is in his sole name.
Also the wife may be able to prevent a charge being put on the property under the married woman property act.
If the property is in joint names and the joint owner is still living in the property he / she has the right to occupy it indefinitely so the value of the joint owners share is nil as nobody will buy half a house with somebody in it.
With regard to putting limits on an amount a person can inherit it would act as a disincentive for a person to work and create wealth if they know their wealth will not go to the son / daughter when they pass away.
Also people may get round the regulations for example by leaving £200,000 to their son, £200,000 to their daughter in law and £200,000 for each of the grandchildren.
With regards to your proposals to take care fees from wealthy children if this happens you will remove the incentive for them to save for retirement if people know the money could be taken for the parent's care fees.
£100,000 may sound a lot but if the children are about to retire or just retired the money could be their retirement nest egg.
Also what would you do if the children are abroad and not subject to UK law.
Another problem could happen here. If one child is in the UK and another is not and if the one who is abroad refuses to pay are you going to make the one in the UK pay all the fees?.
Frank