During the Japanese enthronement celebrations cameras caught Queen Letizia telling Crown Princess Victoria how much she liked the social media postings of the family and how they had to get together soon (during the summer, I believe) if possible which to me says that the two families are friendly with each other. She also seemed to get along splendidly with Prince Daniel and the King and Queen during the state visit last year although, of course, what we saw were them on the job and not them in private.
The Oranjes are also on friendly terms with the Royal family of Jaipur
Princess Diya Kumari even writes in her Facebook post that "Old friendships are the best friendships" so I guess that they go way back.
As if by coincidence the titular Maharaja of Jaipur and his grandmother the Queen Mother Padmini Devi visited the Prince of Wales at Highgrove a few days ago. As shown both in text and in photos it seems that Charles and the Jaipurs have been close for a very long time.
While it is easy to condemn M-C it is obvious that the relationship between the rest of the family and the SRF seems to have survived quite well and some of them are actually close friends.
Asking me to read all biographies of the Dutch royal family without specifying in which this specific claim can be found, isn't that helpful I'm afraid. I don't doubt that you read many books but some sources are more trustworthy than others, so I look forward to the specifics. As you may know, TRF encourages people to back up their claims or opinions with reputable sources. 
Yes, I remember reading about them representing their countries visiting shared interests in the Arctic region. The geography of their countries has meant they, as heirs to their respective thrones have been involved in all sorts of different projects together with Fredrik of Denmark. Over time they became de-facto siblings and each share a common destiny that will serve them in years to come.
Plus they are much more closely related (Victoria and Frederik and Crown Prince Haakon) than some royals of this generation so the sibling relationship is understandable.
Yes, they have been close for years and QEQM and the late Queen Elizabeth were friends with his step grandmother, Maharani Gayatri Devi of Jaipur nee Princess of Cooch Behar (third wife of his great-grandfather, Man Singh II) who was a polo player and horse lover like the late Queen herself. Yes, Padmanabh Singh is Charles’s godson and a few years ago, he was invited to the then Prince of Wales’s birthday at BP.
Baudoin and Fabiola were very close to the Emperor and Empress Emeritus because it was King Baudoin who carried messages from Emperor Akihito to Empress Michiko when she was in Belgium and it makes sense why the Empress herself went to Queen Fabiola’s funeral.
I don’t think or know that the Grimaldis were necessarily looked down on when it came down to Grace and Rainier (I know Queen Frederica of Greece was no fan of them, particularly Grace), but in previous generations that was the case particularly in Queen Victoria’s time when she would never consider a match between one of her descendants and a Grimaldi because they made money from casinos. But these days, in spite of some of the news on them, they are always invited to events even when Grace and Rainier were on the throne.
Every remaining Royal house attended Grace's funeral and Rainier's as well.
The Grimaldis are "only" Serene Highnesses and not Royal highness but I think that counted for more in the past than it does now. All the Royal/Princely houses are an endangered, shrinking species. Every one of them has welcomed commoners into their midst.
None can claim superiority to any other these days-IMO.
In any case, Albert and his family are one of an extremely small handful of rulers who are not dependent upon the goodwill of press and public to stay on their thrones. They are wealthy beyond belief without taxing their subjects. They don't have to account for their time or the way they spend their money. They can do as they please, and that-as well as their glamour and the high drama of their lives- is exactly part of the reason I love watching them.
I don't imagine they are losing any sleep about being "looked down upon" by the others if they indeed are.
