Thank you both for the interesting discussion. I hope it can continue.
To clarify the succession laws, which potentially affected decisions on titles, and my assumptions about them:
I assume that Queen Juliana having sons and daughters would not have altered the history of the succession laws, and the alterations which took place in our history in 1963 and 1983 would still have taken place in 1963 and 1983 in my hypothetical scenario. Please correct me if that assumption is wrong.
I am also assuming that in the hypothetical scenario, Queen Juliana's children would all have married (with parliamentary permission) and had children
after the 1963 alteration but
before the 1983 alteration, so that the titles of the Queen's grandchildren might be affected by the changes of 1963 but would definitely
not be affected by the changes of 1983.
This is the law of succession as it was from 1963 to 1983:
https://www.denederlandsegrondwet.nl/9353000/1/j9vvihlf299q0sr/vi7obqqpnazm
An older sister and her descendants would be superseded by her younger brother and his descendants, but not by further male relatives or their descendants. The line of succession was limited to three degrees of consanguinity of the current monarch. Those who married without acquiring the permission of Parliament lost their right to the throne and their descendants had no place in the line of succession.
The Constitution did not legislate titles or membership of the Royal House.