Sometimes there are issues that are larger than life. The impact goes far beyond one individuals lifestyle or family life. I don't believe Gustav has ever looked at this issue as only who he can or can not marry. He could have married "equal" but what about a possible first son of such a union. The issue of who the heir marries will impact every generation unless they can get that particular clause of the will changed.
The grandfather's will, as Head of the House of Berleberg, applies only to this generation.
Only to Gustav. And European courts have found in similar cases where the Head of the House has placed such restrictions, that these restrictions are fully enforceable, since they do not forbid marriage. They are not a human rights violation. All it says is that the wealth moves on.
The will skipped Gutsav's father Richard as Head of House, although he is the reigning Prince. This was a wealth preservation move, to minimize taxes. The "stuff" went to Prince Richard's son in accordance with the will from the early 1940's, when Prince Richard was still wearing knee breeches and his marriage to Benedickt (and obviously the birth of Gustav) was a good thirty-plus years away.
So the question of whether this goes on to the next generation is
completely moot. Gustav (or whoever replaces Gustav in ownership position of the "stuff") will be the Head of the House and will be allowed to set up inheritance in accordance with their own wishes, wishes that will be as legally binding as the will prepared by the grandfather.
That doesn't mean that Gustav can decide what happens to the stuff now. He's already inherited the Headship of the House, and after his father's death, he becomes reigning Prince. But he is not in control of what happens to it after his death. He can't parcel it out and pass it like after-dinner mints during his life or his father's life, and he can't pass it on to his own children unless they are born of a marriage as stipulated in the will. If he dies without children and without marrying, the stuff goes to the next heir. If he marries within the stipulations of the will, then he gets to pass the stuff on to his heirs in accordance with his own will and desires. If he marries outside of the stipulations of the grandfather's will - under which he has enjoyed a supremely comfortable living and about which he and his family have known since birth - the stuff goes to his cousin (including both the title of Reigning Prince and the Headship of the House.) It could not have been laid out any plainer to Prince Richard, to Princess Benedikt, to Prince Gustav - and very sadly, to Princesses Alexandra and Nathalie. Sadly, because they are completely cut out only by virtue of something beyond their control.
The only question about these restrictions pertains to who is the inheritor under the grandfather's will. Right now, it is Gustav. If it's not Gustav because he marries in contravention of the will itself, then it is his cousin.
Simply stated, this will binds
only the heirs of the grandfather in this generation - specifically Gustav or the next heir after him until one that follows the regulations has been found and the "stuff" has devolved onto that heir. As I have stated previously, that person already exists, already has wide experience in managing similar estates, has married in accordance with the will and - as a nice bonus - has an heir. That would be Bernhard, Prinz zu Sayn-Wittgenstein-Hohenstein, who is the grandson of Richard 4th Fürst zu Sayn-Wittgenstein-Berleburg. Richard 4th Fürst zu Sayn-Wittgenstein-Berleburg is Gustav's great-grandfather, making Bernhard (strictly speaking) Gustav's first cousin once removed.
Other thoughts, in no particular order:
Whether the "stuff" should stay "in this branch" does not take into account the historic nature of the "splitting" of this branch. That split took place only at the level of the shared great-grandfather/grandfather. If Gustav marries his current lover, then the "stuff" goes to the junior branch of the family, and the Berleberg and Hohenstein branches are reunited. I actually think that is a wonderful outcome.
Gustav as "poor?" Heavens! He certainly looks healthy enough to get a job and work for a living. Not only that, but I think that a nice little jointure awaits him even if he turns his back on his inheritance. When I was working at an international bank in Manhattan, we had not one but two such princes working in the bank with very few qualifications except the ability to make introductions. They had very little in the way of money but had sumptuous salaries. I'm sure Gustav's connections wouldn't let him go a-beggin' in the streets, now, let's not be dramatic. Not only that, but the loss of his inheritance would be due wholly to his own choice and his alone. I mean, really, even the fabulously wealthy BRF has members in the third and fourth generations who work for a living, receive no public money, and actually live off their earnings. It's very possible, you know.
Anna, it's likely that the will won't be overturned. Similar court cases have not been. The Head of a House has the absolute right as to who may inherit the property that is his to distribute.
Since there seems to be an uprising about the "cold hard cash" thought, I'll step that up to a less simplistic wording and point out that the will, and Gustav's refusal to marry without getting the "stuff," is a continuation of
wealth preservation. I had been trying to keep this as simple as possible because it seems that many are determined to believe that the grandfather's will forbids a marriage.
It. Does. Not. It just means that Gustav must marry in accordance with the terms of the will - something that is 100% within his control! - or lose the "stuff." Gustav and his family have known the terms of the will for decades.
(I really don't know why letting go of the Harlequin romance aspect of this is so very hard. It's not like any of this was a surprise, or that this is Gustav's first little romance. He was engaged in accordance with the will before, for heaven's sake!)
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Guido's news is interesting. And it does indeed seem cold to me that she would go ahead with a public event so soon after a grief such as this strikes her family. Volcanic ash or no, it's in very poor taste to appear bejeweled and gowned, as though nothing had happened. After all, it wasn't as though her presence either made or broke the event. Shocking in its calculated nature, rather like a triage of self-interest.
Of course, I'm not a mind reader, but perhaps she felt her interests were better served elsewhere than with her family in their grief either in person or in spirit (observing grief privately.) Oh, well. It's not like it was her husband or anything, right?
This is the reason why Carina wore dark gown at theatre. She lost her 2nd brother-in-law, too. Her 1st brother-in-law also died tragically.
I think she looks good for her age. 
