The ECHR ruled against a pair of sisters sharing a home who wanted the inheritance rules to apply to them in the same way as civil partnership or marriage today.
This was an entirely sensible decision. Essentially marriage and civil partnership contain the same rights and responsibilities. One can divorce one's partner in these circumstances. The same cannot be said for siblings.
There may well be questions about the fairness of the inheritance tax system - but they need to be dealt with and looked at entirely separately because they are simply not the same issue. The real aim of the Christian religionists who encouraged this case was to try and downgrade civil partnership and make it less like gay marriage. Unfortunately for them, it is gay marriage. Its just called something different. The template is the same. And that is the way it will stay, whether angry and reactionary peddlers of harmful religionism like it or not.