c In Germany, the owner of an estate has the right to oversee it in any way he/she wishes to. If a person wrote a will leaving his entire fortune to his dog, bypassing his 15 children and wife, it would be perfectly legal (providing he was in sound mind, of course). Basically, in Germany the legal opinion is that a persona is the absolute and undisputed owner of his fortune and how he distributes it or who he names as his heir is entirely up to him.
Actually this is not right, Artemisia. We have what is called the "Pflichtteil"-clause.
Normally an estate (meaning here the whole of one's possessions) is divided by law in several parts which form the "gesetzliche Erbteil" - this "Legal inheritance" is the way the estate must provide for the relatives if no will is being made. Half of it goes to the spouse, the rest is divided through the number of children. Children of late children inherit the part their late parent would have gotten.
E.g. A man was married and had three children. One son predeceased him and left two children. Then the spouse gets half of the inheritance, each child gets a third of the second half = 1/6 and the grandchildren get their fathers 1/6, so each gets 1/12.
Each of these direct line relatives have a right to half of their "legal inheritance". That's what we call "Pflichtteil" - enforcable inheritance.
So in fact a person can only decide about one half of the estate, the other half has be given to the legal heirs.
But of course there are ways around this. In former times a "Fideikommis" was installed, a kind of trust which bound the estate and made it available only to one heir according to primogeniture. Most of these family trusts had such an equality clause.
In 1919, after WWI, in Germany these trusts were ended. But another legal form of trusts were introduced and most head of aristocratic families decided to bring the family fortune into such a family foundation in order to save inheritance tax. The chairman of the board of directos of this family foundation was the Head of the family and he in most cases could make the rules. And these can be discriminating, there's no legal way against it.
As these trusts are legal persons, there is legally no "inheritance", just a change of control of the trust. And just like you cannot legally go against the church and claim that the control over a doecese should be open to men and women, you can do nothing against the stipulation that the chairman of the trust has to marry equally.
As long as we have no information about the legal form the estate is in and the stipulations around it, we cannot say anything about it, really.