No flag for Nikolai, he is not an active member of the DRF. Nor is he a child of the Monarch.
I don't think that rule is chiseled in stone though, it's simply up to the Monarch.
I don't recall much talk, specifically about Nikolai and later Felix, when they were small in regards to their future roles.
It was very much expected that Frederik would eventually marry and given his track-record of having female sweethearts, there were few problems in the horizon regarding off springs. - Even though QMII was actually asked directly whether a future wife of Frederik should be blue-blooded. QMII retorted by replying that she wouldn't demand a blood-sample.
Anyway, for years during the 90's and very early 00's Joachim and Alexandra were the de facto cp-couple, but in regards to roles they had but also very much in the eyes of a wide segment of the public, so while it wasn't perhaps discussed at the coffee tables, the idea of a future king Nikolai wasn't that far off at the time.
As for Ingolf and his branch of the family.
He's brighter than he looks (a DK idiom). He has been the bridge-builder between the two branches of the family, because it is no secret (Ingolf has repeated that in an interview in BB this week BTW) that the transfer of the linage to Frederik IX's children caused quite a lot of bitterness and disappointment in Prince Knud's side of the family. And even though it has been denied, there is little doubt that it strained the relationship between the two brothers. (There has been rumors that Knud to at least some extent blamed Queen Ingrid. She had ambitions on behalf of her children etc. and while Frederik IX no doubt loved his brother, he was also very much a devoted husband and father.)
Now, this is just a thought of mine, QMII was and is fiercely devoted to her father. And being a teen at the time of the transfer in 1953, she would have been able to witness and understand first hand the bitterness and the strain on the family relations at the time and I cannot free myself from the thought that QMII once she became queen, sided totally with her parents.
And perhaps reinforced by the strain of taking over when she was so young, and felt so unprepared, combined with the grief of losing her father, I don't think the Knud side of the family got much sympathy or understanding from QMII. - Queens are only humans and sometimes they act like humans...
Because it is very clear that the two sides of the family did not wear out each others doormats!
It was Ingolf who was the go-between and who managed to reestablish a good relationship with in particular Joachim, but also the rest of QMII's branch.
From interviews we have learned that, while Knud may have been able to understand his brother's position - at least to some extent - there was considerable resentment within his family. Again, children tend to side with their parents.
In this weeks BB interview, mentioned here:
https://www.bt.dk/royale/han-kunne-...e-man-skal-ikke-dvaele-ved-ting-der-alligevel
Ingolf comments on the transfer of linage like this:
Dét er, som det er, og ikke noget, jeg borer i eller bruger tid på. Tidligere var det til tider svært i og for familien, og som Dronningen (Margrethe, red.) så rigtigt sagde i udsendelsen om kong Frederik IX, så var det især en svær tid for 'onkel', altså min far. Men jeg bruger ikke tid på den slags. Man skal ikke dvæle ved ting, der alligevel ikke kan laves om eller gøres noget ved
"It is as it is, and it is not something I go into or spend time on. Previously it was at times difficult within and for the family and as the Queen so rightly said in the documentary about King Frederik IX, it was in particular a difficult time for -uncle,- that is, my father. But I don't spend time on that sort of things. You shouldn't dwell on things that cannot be undone or changed."